draft-ietf-anima-grasp-09.txt

Network Working Group                                         C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                       B. Carpenter, Ed.
Expires: June 18, 2017                                 Univ. of Auckland
                                                             B. Liu, Ed.
                                            Huawei Technologies Co., Ltd
                                                       December 15, 2016


             A Generic Autonomic Signaling Protocol (GRASP)
                       draft-ietf-anima-grasp-09

Abstract

   This document establishes requirements for a signaling protocol that
   enables autonomic devices and autonomic service agents to dynamically
   discover peers, to synchronize state with them, and to negotiate
   parameter settings mutually with them.  The document then defines a
   general protocol for discovery, synchronization and negotiation,
   while the technical objectives for specific scenarios are to be
   described in separate documents.  An Appendix briefly discusses
   existing protocols with comparable features.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 18, 2017.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirement Analysis of Discovery, Synchronization and
       Negotiation . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements for Discovery  . . . . . . . . . . . . . . .   5
     2.2.  Requirements for Synchronization and Negotiation
           Capability  . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Specific Technical Requirements . . . . . . . . . . . . .   9
   3.  GRASP Protocol Overview . . . . . . . . . . . . . . . . . . .  10
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .  10
     3.2.  High Level Deployment Model . . . . . . . . . . . . . . .  12
     3.3.  High Level Design Choices . . . . . . . . . . . . . . . .  13
     3.4.  Quick Operating Overview  . . . . . . . . . . . . . . . .  16
     3.5.  GRASP Protocol Basic Properties and Mechanisms  . . . . .  16
       3.5.1.  Required External Security Mechanism  . . . . . . . .  16
       3.5.2.  Constrained Instances . . . . . . . . . . . . . . . .  17
       3.5.3.  Transport Layer Usage . . . . . . . . . . . . . . . .  19
       3.5.4.  Discovery Mechanism and Procedures  . . . . . . . . .  20
       3.5.5.  Negotiation Procedures  . . . . . . . . . . . . . . .  23
       3.5.6.  Synchronization and Flooding Procedure  . . . . . . .  25
     3.6.  GRASP Constants . . . . . . . . . . . . . . . . . . . . .  27
     3.7.  Session Identifier (Session ID) . . . . . . . . . . . . .  27
     3.8.  GRASP Messages  . . . . . . . . . . . . . . . . . . . . .  28
       3.8.1.  Message Overview  . . . . . . . . . . . . . . . . . .  28
       3.8.2.  GRASP Message Format  . . . . . . . . . . . . . . . .  29
       3.8.3.  Message Size  . . . . . . . . . . . . . . . . . . . .  29
       3.8.4.  Discovery Message . . . . . . . . . . . . . . . . . .  30
       3.8.5.  Discovery Response Message  . . . . . . . . . . . . .  31
       3.8.6.  Request Messages  . . . . . . . . . . . . . . . . . .  32
       3.8.7.  Negotiation Message . . . . . . . . . . . . . . . . .  33
       3.8.8.  Negotiation End Message . . . . . . . . . . . . . . .  33
       3.8.9.  Confirm Waiting     Message . . . . . . . . . . . . .  33
       3.8.10. Synchronization Message . . . . . . . . . . . . . . .  34
       3.8.11. Flood Synchronization Message . . . . . . . . . . . .  34
       3.8.12. Invalid Message . . . . . . . . . . . . . . . . . . .  35
       3.8.13. No Operation Message  . . . . . . . . . . . . . . . .  35
     3.9.  GRASP Options . . . . . . . . . . . . . . . . . . . . . .  36
       3.9.1.  Format of GRASP Options . . . . . . . . . . . . . . .  36
       3.9.2.  Divert Option . . . . . . . . . . . . . . . . . . . .  36
       3.9.3.  Accept Option . . . . . . . . . . . . . . . . . . . .  36



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       3.9.4.  Decline Option  . . . . . . . . . . . . . . . . . . .  37
       3.9.5.  Locator Options . . . . . . . . . . . . . . . . . . .  37
     3.10. Objective Options . . . . . . . . . . . . . . . . . . . .  39
       3.10.1.  Format of Objective Options  . . . . . . . . . . . .  39
       3.10.2.  Objective flags  . . . . . . . . . . . . . . . . . .  40
       3.10.3.  General Considerations for Objective Options . . . .  41
       3.10.4.  Organizing of Objective Options  . . . . . . . . . .  41
       3.10.5.  Experimental and Example Objective Options . . . . .  43
   4.  Implementation Status [RFC Editor: please remove] . . . . . .  43
     4.1.  BUPT C++ Implementation . . . . . . . . . . . . . . . . .  43
     4.2.  Python Implementation . . . . . . . . . . . . . . . . . .  44
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  45
   6.  CDDL Specification of GRASP . . . . . . . . . . . . . . . . .  47
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  49
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  51
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  51
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  51
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  52
   Appendix A.  Open Issues [RFC Editor: Please remove if empty] . .  55
   Appendix B.  Closed Issues [RFC Editor: Please remove]  . . . . .  55
   Appendix C.  Change log [RFC Editor: Please remove] . . . . . . .  63
   Appendix D.  Example Message Formats  . . . . . . . . . . . . . .  69
     D.1.  Discovery Example . . . . . . . . . . . . . . . . . . . .  69
     D.2.  Flood Example . . . . . . . . . . . . . . . . . . . . . .  70
     D.3.  Synchronization Example . . . . . . . . . . . . . . . . .  70
     D.4.  Simple Negotiation Example  . . . . . . . . . . . . . . .  70
     D.5.  Complete Negotiation Example  . . . . . . . . . . . . . .  71
   Appendix E.  Capability Analysis of Current Protocols . . . . . .  72
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  75

1.  Introduction

   The success of the Internet has made IP-based networks bigger and
   more complicated.  Large-scale ISP and enterprise networks have
   become more and more problematic for human based management.  Also,
   operational costs are growing quickly.  Consequently, there are
   increased requirements for autonomic behavior in the networks.
   General aspects of autonomic networks are discussed in [RFC7575] and
   [RFC7576].

   One approach is to largely decentralize the logic of network
   management by migrating it into network elements.  A reference model
   for autonomic networking on this basis is given in
   [I-D.ietf-anima-reference-model].  The reader should consult this
   document to understand how various autonomic components fit together.
   In order to fulfil autonomy, devices that embody Autonomic Service
   Agents (ASAs, [RFC7575]) have specific signaling requirements.  In
   particular they need to discover each other, to synchronize state



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   with each other, and to negotiate parameters and resources directly
   with each other.  There is no limitation on the types of parameters
   and resources concerned, which can include very basic information
   needed for addressing and routing, as well as anything else that
   might be configured in a conventional non-autonomic network.  The
   atomic unit of discovery, synchronization or negotiation is referred
   to as a technical objective, i.e, a configurable parameter or set of
   parameters (defined more precisely in Section 3.1).

   Following this Introduction, Section 2 describes the requirements for
   discovery, synchronization and negotiation.  Negotiation is an
   iterative process, requiring multiple message exchanges forming a
   closed loop between the negotiating entities.  In fact, these
   entities are ASAs, normally but not necessarily in different network
   devices.  State synchronization, when needed, can be regarded as a
   special case of negotiation, without iteration.  Section 3.3
   describes a behavior model for a protocol intended to support
   discovery, synchronization and negotiation.  The design of GeneRic
   Autonomic Signaling Protocol (GRASP) in Section 3 of this document is
   mainly based on this behavior model.  The relevant capabilities of
   various existing protocols are reviewed in Appendix E.

   The proposed discovery mechanism is oriented towards synchronization
   and negotiation objectives.  It is based on a neighbor discovery
   process, but also supports diversion to off-link peers.  There is no
   assumption of any particular form of network topology.  When a device
   starts up with no pre-configuration, it has no knowledge of the
   topology.  The protocol itself is capable of being used in a small
   and/or flat network structure such as a small office or home network
   as well as a professionally managed network.  Therefore, the
   discovery mechanism needs to be able to allow a device to bootstrap
   itself without making any prior assumptions about network structure.

   Because GRASP can be used to perform a decision process among
   distributed devices or between networks, it must run in a secure and
   strongly authenticated environment.

   It is understood that in realistic deployments, not all devices will
   support GRASP.  It is expected that some autonomic service agents
   will directly manage a group of non-autonomic nodes, and that other
   non-autonomic nodes will be managed traditionally.  Such mixed
   scenarios are not discussed in this specification.

2.  Requirement Analysis of Discovery, Synchronization and Negotiation

   This section discusses the requirements for discovery, negotiation
   and synchronization capabilities.  The primary user of the protocol
   is an autonomic service agent (ASA), so the requirements are mainly



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   expressed as the features needed by an ASA.  A single physical device
   might contain several ASAs, and a single ASA might manage several
   technical objectives.  If a technical objective is managed by several
   ASAs, any necessary coordination is outside the scope of the
   signaling protocol itself.

   Note that requirements for ASAs themselves, such as the processing of
   Intent [RFC7575] or interfaces for coordination between ASAs are out
   of scope for the present document.

2.1.  Requirements for Discovery

   D1.  ASAs may be designed to manage anything, as required in
   Section 2.2.  A basic requirement is therefore that the protocol can
   represent and discover any kind of technical objective among
   arbitrary subsets of participating nodes.

   In an autonomic network we must assume that when a device starts up
   it has no information about any peer devices, the network structure,
   or what specific role it must play.  The ASA(s) inside the device are
   in the same situation.  In some cases, when a new application session
   starts up within a device, the device or ASA may again lack
   information about relevant peers.  For example, it might be necessary
   to set up resources on multiple other devices, coordinated and
   matched to each other so that there is no wasted resource.  Security
   settings might also need updating to allow for the new device or
   user.  The relevant peers may be different for different technical
   objectives.  Therefore discovery needs to be repeated as often as
   necessary to find peers capable of acting as counterparts for each
   objective that a discovery initiator needs to handle.  From this
   background we derive the next three requirements:

   D2.  When an ASA first starts up, it has no knowledge of the specific
   network to which it is attached.  Therefore the discovery process
   must be able to support any network scenario, assuming only that the
   device concerned is bootstrapped from factory condition.

   D3.  When an ASA starts up, it must require no configured location
   information about any peers in order to discover them.

   D4.  If an ASA supports multiple technical objectives, relevant peers
   may be different for different discovery objectives, so discovery
   needs to be performed separately to find counterparts for each
   objective.  Thus, there must be a mechanism by which an ASA can
   separately discover peer ASAs for each of the technical objectives
   that it needs to manage, whenever necessary.





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   D5.  Following discovery, an ASA will normally perform negotiation or
   synchronization for the corresponding objectives.  The design should
   allow for this by conveniently linking discovery to negotiation and
   synchronization.  It may provide an optional mechanism to combine
   discovery and negotiation/synchronization in a single call.

   D6.  Some objectives may only be significant on the local link, but
   others may be significant across the routed network and require off-
   link operations.  Thus, the relevant peers might be immediate
   neighbors on the same layer 2 link, or they might be more distant and
   only accessible via layer 3.  The mechanism must therefore provide
   both on-link and off-link discovery of ASAs supporting specific
   technical objectives.

   D7.  The discovery process should be flexible enough to allow for
   special cases, such as the following:

   o  During initialisation, a device must be able to establish mutual
      trust with the rest of the network and join an authentication
      mechanism.  Although this will inevitably start with a discovery
      action, it is a special case precisely because trust is not yet
      established.  This topic is the subject of
      [I-D.ietf-anima-bootstrapping-keyinfra].  We require that once
      trust has been established for a device, all ASAs within the
      device inherit the device's credentials and are also trusted.

   o  Depending on the type of network involved, discovery of other
      central functions might be needed, such as the Network Operations
      Center (NOC) [I-D.ietf-anima-stable-connectivity].  The protocol
      must be capable of supporting such discovery during
      initialisation, as well as discovery during ongoing operation.

   D8.  The discovery process must not generate excessive traffic and
   must take account of sleeping nodes.

   D9.  There must be a mechanism for handling stale discovery results.

2.2.  Requirements for Synchronization and Negotiation Capability

   As background, consider the example of routing protocols, the closest
   approximation to autonomic networking already in widespread use.
   Routing protocols use a largely autonomic model based on distributed
   devices that communicate repeatedly with each other.  The focus is
   reachability, so current routing protocols mainly consider simple
   link status, i.e., up or down, and an underlying assumption is that
   all nodes need a consistent view of the network topology in order for
   the routing algorithm to converge.  Thus, routing is mainly based on
   information synchronization between peers, rather than on bi-



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   directional negotiation.  Other information, such as latency,
   congestion, capacity, and particularly unused capacity, would be
   helpful to get better path selection and utilization rate, but is not
   normally used in distributed routing algorithms.  Additionally,
   autonomic networks need to be able to manage many more dimensions,
   such as security settings, power saving, load balancing, etc.  Status
   information and traffic metrics need to be shared between nodes for
   dynamic adjustment of resources and for monitoring purposes.  While
   this might be achieved by existing protocols when they are available,
   the new protocol needs to be able to support parameter exchange,
   including mutual synchronization, even when no negotiation as such is
   required.  In general, these parameters do not apply to all
   participating nodes, but only to a subset.

   SN1.  A basic requirement for the protocol is therefore the ability
   to represent, discover, synchronize and negotiate almost any kind of
   network parameter among selected subsets of participating nodes.

   SN2.  Negotiation is a request/response process that must be
   guaranteed to terminate (with success or failure) and if necessary it
   must contain tie-breaking rules for each technical objective that
   requires them.  While these must be defined specifically for each use
   case, the protocol should have some general mechanisms in support of
   loop and deadlock prevention, such as hop count limits or timeouts.

   SN3.  Synchronization might concern small groups of nodes or very
   large groups.  Different solutions might be needed at different
   scales.

   SN4.  To avoid "reinventing the wheel", the protocol should be able
   to encapsulate the data formats used by existing configuration
   protocols (such as NETCONF/YANG) in cases where that is convenient.

   SN5.  Human intervention in complex situations is costly and error-
   prone.  Therefore, synchronization or negotiation of parameters
   without human intervention is desirable whenever the coordination of
   multiple devices can improve overall network performance.  It
   therefore follows that the protocol, as part of the Autonomic
   Networking Infrastructure, should be capable of running in any device
   that would otherwise need human intervention.  The issue of running
   in constrained nodes is discussed in
   [I-D.ietf-anima-reference-model].

   SN6.  Human intervention in large networks is often replaced by use
   of a top-down network management system (NMS).  It therefore follows
   that the protocol, as part of the Autonomic Networking
   Infrastructure, should be capable of running in any device that would




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   otherwise be managed by an NMS, and that it can co-exist with an NMS,
   and with protocols such as SNMP and NETCONF.

   SN7.  Some features are expected to be implemented by individual
   ASAs, but the protocol must be general enough to allow them:

   o  Dependencies and conflicts: In order to decide upon a
      configuration for a given device, the device may need information
      from neighbors.  This can be established through the negotiation
      procedure, or through synchronization if that is sufficient.
      However, a given item in a neighbor may depend on other
      information from its own neighbors, which may need another
      negotiation or synchronization procedure to obtain or decide.
      Therefore, there are potential dependencies and conflicts among
      negotiation or synchronization procedures.  Resolving dependencies
      and conflicts is a matter for the individual ASAs involved.  To
      allow this, there need to be clear boundaries and convergence
      mechanisms for negotiations.  Also some mechanisms are needed to
      avoid loop dependencies.  In such a case, the protocol's role is
      limited to bilateral signaling between ASAs.

   o  Recovery from faults and identification of faulty devices should
      be as automatic as possible.  The protocol's role is limited to
      discovery, synchronization and negotiation.  These processes can
      occur at any time, and an ASA may need to repeat any of these
      steps when the ASA detects an anomaly such as a negotiation
      counterpart failing.

   o  Since the goal is to minimize human intervention, it is necessary
      that the network can in effect "think ahead" before changing its
      parameters.  One aspect of this is an ASA that relies on a
      knowledge base to predict network behavior.  This is out of scope
      for the signaling protocol.  However, another aspect is
      forecasting the effect of a change by a "dry run" negotiation
      before actually installing the change.  This will be an
      application of the protocol rather than a feature of the protocol
      itself.

   o  Management logging, monitoring, alerts and tools for intervention
      are required.  However, these can only be features of individual
      ASAs.  Another document [I-D.ietf-anima-stable-connectivity]
      discusses how such agents may be linked into conventional OAM
      systems via an Autonomic Control Plane
      [I-D.ietf-anima-autonomic-control-plane].

   SN8.  The protocol will be able to deal with a wide variety of
   technical objectives, covering any type of network parameter.
   Therefore the protocol will need a flexible and easily extensible



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   format for describing objectives.  At a later stage it may be
   desirable to adopt an explicit information model.  One consideration
   is whether to adopt an existing information model or to design a new
   one.

2.3.  Specific Technical Requirements

   T1.  It should be convenient for ASA designers to define new
   technical objectives and for programmers to express them, without
   excessive impact on run-time efficiency and footprint.  In
   particular, it should be possible for ASAs to be implemented
   independently of each other as user space programs rather than as
   kernel code.  The classes of device in which the protocol might run
   is discussed in [I-D.ietf-anima-reference-model].

   T2.  The protocol should be easily extensible in case the initially
   defined discovery, synchronization and negotiation mechanisms prove
   to be insufficient.

   T3.  To be a generic platform, the protocol payload format should be
   independent of the transport protocol or IP version.  In particular,
   it should be able to run over IPv6 or IPv4.  However, some functions,
   such as multicasting on a link, might need to be IP version
   dependent.  In case of doubt, IPv6 should be preferred.

   T4.  The protocol must be able to access off-link counterparts via
   routable addresses, i.e., must not be restricted to link-local
   operation.

   T5.  It must also be possible for an external discovery mechanism to
   be used, if appropriate for a given technical objective.  In other
   words, GRASP discovery must not be a prerequisite for GRASP
   negotiation or synchronization.

   T6.  The protocol must be capable of supporting multiple simultaneous
   operations, especially when wait states occur.

   T7.  Intent: There must be provision for general Intent rules to be
   applied by all devices in the network (e.g., security rules, prefix
   length, resource sharing rules).  However, Intent distribution might
   not use the signaling protocol itself, but its design should not
   exclude such use.

   T8.  Management monitoring, alerts and intervention: Devices should
   be able to report to a monitoring system.  Some events must be able
   to generate operator alerts and some provision for emergency
   intervention must be possible (e.g.  to freeze synchronization or
   negotiation in a mis-behaving device).  These features might not use



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   the signaling protocol itself, but its design should not exclude such
   use.

   T9.  The protocol needs to be fully secured against forged messages
   and man-in-the middle attacks, and secured as much as reasonably
   possible against denial of service attacks.  It needs to be capable
   of encryption in order to resist unwanted monitoring.  However, it is
   not required that the protocol itself provides these security
   features; it may depend on an existing secure environment.

3.  GRASP Protocol Overview

3.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key
   words.

   This document uses terminology defined in [RFC7575].

   The following additional terms are used throughout this document:

   o  Autonomic Device: identical to Autonomic Node.

   o  Discovery: a process by which an ASA discovers peers according to
      a specific discovery objective.  The discovery results may be
      different according to the different discovery objectives.  The
      discovered peers may later be used as negotiation counterparts or
      as sources of synchronization data.

   o  Negotiation: a process by which two ASAs interact iteratively to
      agree on parameter settings that best satisfy the objectives of
      both ASAs.

   o  State Synchronization: a process by which ASAs interact to receive
      the current state of parameter values stored in other ASAs.  This
      is a special case of negotiation in which information is sent but
      the ASAs do not request their peers to change parameter settings.
      All other definitions apply to both negotiation and
      synchronization.

   o  Technical Objective (usually abbreviated as Objective): A
      technical objective is a configurable parameter or set of
      parameters of some kind, which occurs in three contexts:



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      Discovery, Negotiation and Synchronization.  In the protocol, an
      objective is represented by an identifier and, if relevant, a
      value.  Normally, a given objective will not occur in negotiation
      and synchronization contexts simultaneously.

      *  One ASA may support multiple independent objectives.

      *  The parameter described by a given objective is naturally based
         on a specific service or function or action.  It may in
         principle be anything that can be set to a specific logical,
         numerical or string value, or a more complex data structure, by
         a network node.  That node is generally expected to contain an
         ASA which may itself manage subsidiary non-autonomic nodes.

      *  Discovery Objective: an objective in the process of discovery.
         Its value may be undefined.

      *  Synchronization Objective: an objective whose specific
         technical content needs to be synchronized among two or more
         ASAs.

      *  Negotiation Objective: an objective whose specific technical
         content needs to be decided in coordination with another ASA.

      A detailed discussion of objectives, including their format, is
      found in Section 3.10.

   o  Discovery Initiator: an ASA that spontaneously starts discovery by
      sending a discovery message referring to a specific discovery
      objective.

   o  Discovery Responder: a peer that either contains an ASA supporting
      the discovery objective indicated by the discovery initiator, or
      caches the locator(s) of the ASA(s) supporting the objective.  It
      sends a Discovery Response, as described later.

   o  Synchronization Initiator: an ASA that spontaneously starts
      synchronization by sending a request message referring to a
      specific synchronization objective.

   o  Synchronization Responder: a peer ASA which responds with the
      value of a synchronization objective.

   o  Negotiation Initiator: an ASA that spontaneously starts
      negotiation by sending a request message referring to a specific
      negotiation objective.





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   o  Negotiation Counterpart: a peer with which the Negotiation
      Initiator negotiates a specific negotiation objective.

3.2.  High Level Deployment Model

   It is expected that a GRASP implementation will reside in an
   autonomic node that also contains both the appropriate security
   environment, preferably the Autonomic Control Plane (ACP)
   [I-D.ietf-anima-autonomic-control-plane], and one or more Autonomic
   Service Agents (ASAs).  In the minimal case of a single-purpose
   device, these three components might be fully integrated.  A more
   common model is expected to be a multi-purpose device capable of
   containing several ASAs.  In this case it is expected that the ACP,
   GRASP and the ASAs will be implemented as separate processes, which
   are probably multi-threaded to support asynchronous and simultaneous
   operations.  It is expected that GRASP will access the ACP by using a
   typical socket interface.  A well defined Application Programming
   Interface (API) will be needed between GRASP and the ASAs.  In some
   implementations, ASAs would run in user space with a GRASP library
   providing the API, and this library would in turn communicate via
   system calls with core GRASP functions.  For further details of
   possible deployment models, see [I-D.ietf-anima-reference-model].

   A GRASP instance must be aware of its network interfaces, and of its
   own global-scope and link-local addresses.  In the presence of the
   ACP, such information will be available from the adjacency table
   discussed in [I-D.ietf-anima-reference-model].  In other cases, GRASP
   must determine such information for itself.  Details depend on the
   operating system.

   Because GRASP needs to work whatever happens, especially during
   bootstrapping and during fault conditions, it is essential that every
   implementation is as robust as possible.  For example, discovery
   failures, or any kind of socket error at any time, must not cause
   irrecoverable failures in GRASP itself, and must return suitable
   error codes through the API so that ASAs can also recover.

   GRASP must always start up correctly after a system restart.  All run
   time error conditions, and events such as address renumbering,
   network interface failures, and CPU sleep/wake cycles, must be
   handled in such a way that GRASP will still operate correctly and
   securely (Section 3.5.1) afterwards.

   An autonomic node will normally run a single instance of GRASP, used
   by multiple ASAs.  However, scenarios where multiple instances of
   GRASP run in a single node, perhaps with different security
   properties, are not excluded.  In this case, each instance MUST




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   listen independently for GRASP link-local multicasts in order for
   discovery and flooding to work correctly.

3.3.  High Level Design Choices

   This section describes a behavior model and design choices for GRASP,
   supporting discovery, synchronization and negotiation, to act as a
   platform for different technical objectives.

   o  A generic platform

      The protocol is designed as a generic platform, which is
      independent from the synchronization or negotiation contents.  It
      takes care of the general intercommunication between counterparts.
      The technical contents will vary according to the various
      technical objectives and the different pairs of counterparts.


   o  The protocol is expected to form part of an Autonomic Networking
      Infrastructure [I-D.ietf-anima-reference-model].  It will provide
      services to ASAs via a suitable application programming interface
      (API), which will reflect the protocol elements but will not
      necessarily be in one-to-one correspondence to them.  This API is
      out of scope for the present document.


   o  It is normally expected that a single main instance of GRASP will
      exist in an autonomic node, and that the protocol engine and each
      ASA will run as independent asynchronous processes.  However,
      separate GRASP instances may exist for security-related reasons
      (Section 3.5.2).


   o  Security infrastructure and trust relationship

      Because this negotiation protocol may directly cause changes to
      device configurations and bring significant impacts to a running
      network, this protocol is required to run within an existing
      secure environment with strong authentication.  As a design
      choice, the protocol itself is not provided with built-in security
      functionality.

      On the other hand, a limited negotiation model might be deployed
      based on a limited trust relationship such as that between two
      administrative domains.  ASAs might then exchange limited
      information and negotiate some particular configurations.





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   o  Discovery, synchronization and negotiation are designed together.

      The discovery method and the synchronization and negotiation
      methods are designed in the same way and can be combined when this
      is useful, allowing a rapid mode of operation described in
      Section 3.5.4.  These processes can also be performed
      independently when appropriate.

      *  Thus, for some objectives, especially those concerned with
         application layer services, another discovery mechanism such as
         the future DNS Service Discovery [RFC7558] MAY be used.  The
         choice is left to the designers of individual ASAs.


   o  A uniform pattern for technical objectives

      The synchronization and negotiation objectives are defined
      according to a uniform pattern.  The values that they contain
      could be carried either in a simple binary format or in a complex
      object format.  The basic protocol design uses the Concise Binary
      Object Representation (CBOR) [RFC7049], which is readily
      extensible for unknown future requirements.


   o  A flexible model for synchronization

      GRASP supports bilateral synchronization, which could be used to
      perform synchronization among a small number of nodes.  It also
      supports an unsolicited flooding mode when large groups of nodes,
      possibly including all autonomic nodes, need data for the same
      technical objective.

      *  There may be some network parameters for which a more
         traditional flooding mechanism such as DNCP [RFC7787] is
         considered more appropriate.  GRASP can coexist with DNCP.


   o  A simple initiator/responder model for negotiation

      Multi-party negotiations are very complicated to model and cannot
      readily be guaranteed to converge.  GRASP uses a simple bilateral
      model and can support multi-party negotiations by indirect steps.


   o  Organizing of synchronization or negotiation content

      The technical content transmitted by GRASP will be organized
      according to the relevant function or service.  The objectives for



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      different functions or services are kept separate, because they
      may be negotiated or synchronized with different counterparts or
      have different response times.  Thus a normal arrangement would be
      a single ASA managing a small set of closely related objectives,
      with a version of that ASA in each relevant autonomic node.
      Further discussion of this aspect is out of scope for the current
      document.


   o  Requests and responses in negotiation procedures

      The initiator can negotiate a specific negotiation objective with
      relevant counterpart ASAs.  It can request relevant information
      from a counterpart so that it can coordinate its local
      configuration.  It can request the counterpart to make a matching
      configuration.  It can request simulation or forecast results by
      sending some dry run conditions.

      Beyond the traditional yes/no answer, the responder can reply with
      a suggested alternative value for the objective concerned.  This
      would start a bi-directional negotiation ending in a compromise
      between the two ASAs.


   o  Convergence of negotiation procedures

      To enable convergence, when a responder suggests a new value or
      condition in a negotiation step reply, it should be as close as
      possible to the original request or previous suggestion.  The
      suggested value of later negotiation steps should be chosen
      between the suggested values from the previous two steps.  GRASP
      provides mechanisms to guarantee convergence (or failure) in a
      small number of steps, i.e. a timeout and a maximum number of
      iterations.



   o  Extensibility

      GRASP does not have a version number.  In most cases new semantics
      will be added by defining new synchronization or negotiation
      objectives.  However, the protocol could be extended by adding new
      message types and options in future.








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3.4.  Quick Operating Overview

   GRASP is expected to run as an operating system core module,
   providing an API (such as [I-D.liu-anima-grasp-api]) to interface to
   less privileged ASAs.  Thus ASAs may operate without special
   privilege, unless they need it for other reasons (such as configuring
   IP addresses or manipulating routing tables).

   The GRASP mechanisms used by the ASA are built around GRASP
   objectives defined as data structures containing administrative
   information such as the objective's unique name, and its current
   value.  The format and size of the value is not restricted by the
   protocol, except that it must be possible to serialise it for
   transmission in CBOR, which is no restriction at all in practice.

   The GRASP provides the following mechanisms:

   o  A discovery mechanism (M_DISCOVERY, M_RESPONSE), by which an ASA
      can discover other ASAs supporting a given objective.

   o  A negotiation request mechanism (M_REQ_NEG), by which an ASA can
      start negotiation of an objective with a counterpart ASA.  Once a
      negotiation has started, the process is symmetrical, and there is
      a negotiation step message (M_NEGOTIATE) for each ASA to use in
      turn.  Two other functions support negotiating steps (M_WAIT,
      M_END).

   o  A synchronization mechanism (M_REQ_SYN), by which an ASA can
      request the current value of an objective from a counterpart ASA.
      With this, there is a corresponding response function (M_SYNCH)
      for an ASA that wishes to respond to synchronization requests.

   o  A flood mechanism (M_FLOOD), by which an ASA can cause the current
      value of an objective to be flooded throughout the AN so that any
      ASA can receive it.  One application of this is to act as an
      announcement, avoiding the need for discovery of a widely
      applicable objective.

   Some example messages and simple message flows are provided in
   Appendix D.

3.5.  GRASP Protocol Basic Properties and Mechanisms

3.5.1.  Required External Security Mechanism

   The protocol SHOULD always run within a secure Autonomic Control
   Plane (ACP) [I-D.ietf-anima-autonomic-control-plane].  The ACP is
   assumed to carry all messages securely, including link-local



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   multicast if possible.  A GRASP implementation MUST verify whether
   the ACP is operational.

   If there is no ACP, the protocol MUST use another form of strong
   authentication and SHOULD use a form of strong encryption.  See
   Section 3.5.2.1 for further discussion.

   The ACP, or in its absence another security mechanism, sets the
   boundary within which nodes are trusted as GRASP peers.  A GRASP
   implementation MUST refuse to execute GRASP synchronization and
   negotiation functions if there is neither an operational ACP nor
   another secure environment.

   Link-local multicast is used for discovery messages.  Responses to
   discovery messages MUST be secured, with one exception mentioned in
   the next section.

3.5.2.  Constrained Instances

   This section describes some examples of cases where additional
   instances of GRASP subject to certain constraints are appropriate.

3.5.2.1.  No ACP

   As mentioned in Section 3.3, some GRASP operations might be performed
   across an administrative domain boundary by mutual agreement, without
   the benefit of an ACP.  Such operations MUST be confined to a
   separate instance of GRASP with its own copy of all GRASP data
   structures.  Messages MUST be authenticated and SHOULD be encrypted.
   TLS [RFC5246] and DTLS [RFC6347] based on a Public Key Infrastructure
   (PKI) [RFC5280] are RECOMMENDED for this purpose.  Further details
   are out of scope for this document.

3.5.2.2.  Discovery Unsolicited Link-Local

   Some services may need to use insecure GRASP discovery, response and
   flood messages without being able to use pre-existing security
   associations.  Such operations being intrinsically insecure, they
   need to be confined to link-local use to minimise the risk of
   malicious actions.  Possible examples include discovery of candidate
   ACP neighbors [I-D.ietf-anima-autonomic-control-plane], discovery of
   bootstrap proxies [I-D.ietf-anima-bootstrapping-keyinfra] or perhaps
   initialisation services in networks using GRASP without being fully
   autonomic (e.g., no ACP).  Such usage MUST be limited to link-local
   operations and MUST be confined to a separate insecure instance of
   GRASP with its own copy of all GRASP data structures.  This instance
   is nicknamed DULL - Discovery Unsolicited Link-Local.




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   The detailed rules for the DULL instance of GRASP are as follows:

   o  An initiator MUST only send Discovery or Flood Synchronization
      link-local multicast messages with a loop count of 1.  A responder
      SHOULD NOT send a Discovery Response message unless it cannot be
      avoided.  Other GRASP message types MUST NOT be sent.

   o  A responder MUST silently discard any message whose loop count is
      not 1.

   o  A responder MUST silently discard any message referring to a GRASP
      Objective that is not directly part of a service that requires
      this insecure mode.

   o  A responder MUST NOT relay any multicast messages.

   o  A Discovery Response MUST indicate a link-local address.

   o  A Discovery Response MUST NOT include a Divert option.

   o  A node MUST silently discard any message whose source address is
      not link-local.

   GRASP traffic SHOULD be minimized by using only Flood Synchronization
   to announce objectives and their associated locators, rather than by
   using Discovery and Response.  Further details are out of scope for
   this document

3.5.2.3.  Secure Only Neighbor Negotiation

   Some services might use insecure on-link operations as in DULL, but
   also use unicast synchronization or negotiation operations protected
   by TLS.  A separate instance of GRASP is used, with its own copy of
   all GRASP data structures.  This instance is nicknamed SONN - Secure
   Only Neighbor Negotiation.

   The detailed rules for the SONN instance of GRASP are as follows:

   o  Any type of GRASP message MAY be sent.

   o  An initiator MUST send any Discovery or Flood Synchronization
      link-local multicast messages with a loop count of 1.

   o  A responder MUST silently discard any Discovery or Flood
      Synchronization message whose loop count is not 1.

   o  A responder MUST silently discard any message referring to a GRASP
      Objective that is not directly part of the service concerned.



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   o  A responder MUST NOT relay any multicast messages.

   o  A Discovery Response MUST indicate a link-local address.

   o  A Discovery Response MUST NOT include a Divert option.

   o  A node MUST silently discard any message whose source address is
      not link-local.

   Further details, including TLS and PKI usage, are out of scope for
   this document.

3.5.3.  Transport Layer Usage

   GRASP discovery and flooding messages are designed for use over link-
   local multicast UDP.  They MUST NOT be fragmented, and therefore MUST
   NOT exceed the link MTU size.  Nothing in principle prevents them
   from working over some other method of sending packets to all on-link
   neighbors, but this is out of scope for the present specification.

   All other GRASP messages are unicast and could in principle run over
   any transport protocol.  An implementation MUST support use of TCP.
   It MAY support use of another transport protocol.  However, GRASP
   itself does not provide for error detection or retransmission.  Use
   of an unreliable transport protocol is therefore NOT RECOMMENDED.

   Nevertheless, when running within a secure ACP on reliable
   infrastructure, UDP MAY be used for unicast messages not exceeding
   the minimum IPv6 path MTU; however, TCP MUST be used for longer
   messages.  In other words, IPv6 fragmentation is avoided.  If a node
   receives a UDP message but the reply is too long, it MUST open a TCP
   connection to the peer for the reply.  Note that when the network is
   under heavy load or in a fault condition, UDP might become
   unreliable.  Since this is when autonomic functions are most
   necessary, automatic fallback to TCP MUST be implemented.  The
   simplest implementation is therefore to use only TCP.

   For considerations when running without an ACP, see Section 3.5.2.1.

   For link-local multicast, the GRASP protocol listens to the well-
   known GRASP Listen Port (Section 3.6).  For unicast transport
   sessions used for discovery responses, synchronization and
   negotiation, the ASA concerned normally listens on its own
   dynamically assigned ports, which are communicated to its peers
   during discovery.  However, a minimal implementation MAY use the
   GRASP Listen Port for this purpose.





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3.5.4.  Discovery Mechanism and Procedures

3.5.4.1.  Separated discovery and negotiation mechanisms

   Although discovery and negotiation or synchronization are defined
   together in GRASP, they are separate mechanisms.  The discovery
   process could run independently from the negotiation or
   synchronization process.  Upon receiving a Discovery (Section 3.8.4)
   message, the recipient node should return a response message in which
   it either indicates itself as a discovery responder or diverts the
   initiator towards another more suitable ASA.

   The discovery action (M_DISCOVERY) will normally be followed by a
   negotiation (M_REQ_NEG) or synchronization (M_REQ_SYN) action.  The
   discovery results could be utilized by the negotiation protocol to
   decide which ASA the initiator will negotiate with.

   The initiator of a discovery action for a given objective need not be
   capable of responding to that objective as a Negotiation Counterpart,
   as a Synchronization Responder or as source for flooding.  For
   example, an ASA might perform discovery even if it only wishes to act
   a Synchronization Initiator or Negotiation Initiator.  Such an ASA
   does not itself need to respond to discovery messages.

   It is also entirely possible to use GRASP discovery without any
   subsequent negotiation or synchronization action.  In this case, the
   discovered objective is simply used as a name during the discovery
   process and any subsequent operations between the peers are outside
   the scope of GRASP.

3.5.4.2.  Discovery Overview

   A complete discovery process will start with a multicast (of
   M_DISCOVERY) on the local link.  On-link neighbors supporting the
   discovery objective will respond directly (with M_RESPONSE).  A
   neighbor with multiple interfaces will respond with a cached
   discovery response if any.  However, it SHOULD NOT respond with a
   cached response on an interface if it learnt that information from
   the same interface.  If it has no cached response, it will relay the
   discovery on its other interfaces, for example reaching a higher-
   level gateway in a hierarchical network.  If a node receiving the
   relayed discovery supports the discovery objective, it will respond
   to the relayed discovery.  If it has a cached response, it will
   respond with that.  If not, it will repeat the discovery process,
   which thereby becomes recursive.  The loop count and timeout will
   ensure that the process ends.





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   Exceptionally, a Discovery message MAY be sent unicast (via UDP or
   TCP) to a peer node, which will then proceed exactly as if the
   message had been multicast, except that when TCP is used, the
   response will be on the same socket as the query.  However, this mode
   does not guarantee successful discovery in the general case.

3.5.4.3.  Discovery Procedures

   Discovery starts as an on-link operation.  The Divert option can tell
   the discovery initiator to contact an off-link ASA for that discovery
   objective.  Every Discovery message is sent by a discovery initiator
   via UDP to the ALL_GRASP_NEIGHBOR link-local multicast address
   (Section 3.6).  Every network device that supports GRASP always
   listens to a well-known UDP port to capture the discovery messages.
   Because this port is unique in a device, this is a function of the
   GRASP core and not of an individual ASA.  As a result, each ASA will
   need to register the objectives that it supports with the GRASP core.

   If an ASA in a neighbor device supports the requested discovery
   objective, the device SHOULD respond to the link-local multicast with
   a unicast Discovery Response message (Section 3.8.5) with locator
   option(s), unless it is temporarily unavailable.  Otherwise, if the
   neighbor has cached information about an ASA that supports the
   requested discovery objective (usually because it discovered the same
   objective before), it SHOULD respond with a Discovery Response
   message with a Divert option pointing to the appropriate Discovery
   Responder.

   If a device has no information about the requested discovery
   objective, and is not acting as a discovery relay (see below) it MUST
   silently discard the Discovery message.

   If no discovery response is received within a reasonable timeout
   (default GRASP_DEF_TIMEOUT milliseconds, Section 3.6), the Discovery
   message MAY be repeated, with a newly generated Session ID
   (Section 3.7).  An exponential backoff SHOULD be used for subsequent
   repetitions, to limit the load during busy periods.  Frequent
   repetition might be symptomatic of a denial of service attack.

   After a GRASP device successfully discovers a locator for a Discovery
   Responder supporting a specific objective, it MUST cache this
   information, including the interface identifier via which it was
   discovered.  This cache record MAY be used for future negotiation or
   synchronization, and the locator SHOULD be passed on when appropriate
   as a Divert option to another Discovery Initiator.

   The cache mechanism MUST include a lifetime for each entry.  The
   lifetime is derived from a time-to-live (ttl) parameter in each



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   Discovery Response message.  Cached entries MUST be ignored or
   deleted after their lifetime expires.  In some environments,
   unplanned address renumbering might occur.  In such cases, the
   lifetime SHOULD be short compared to the typical address lifetime and
   a mechanism to flush the discovery cache SHOULD be implemented.  The
   discovery mechanism needs to track the node's current address to
   ensure that Discovery Responses always indicate the correct address.

   If multiple Discovery Responders are found for the same objective,
   they SHOULD all be cached, unless this creates a resource shortage.
   The method of choosing between multiple responders is an
   implementation choice.  This choice MUST be available to each ASA but
   the GRASP implementation SHOULD provide a default choice.

   Because Discovery Responders will be cached in a finite cache, they
   might be deleted at any time.  In this case, discovery will need to
   be repeated.  If an ASA exits for any reason, its locator might still
   be cached for some time, and attempts to connect to it will fail.
   ASAs need to be robust in these circumstances.

3.5.4.4.  Discovery Relaying

   A GRASP instance with multiple link-layer interfaces (typically
   running in a router) MUST support discovery on all interfaces.  We
   refer to this as a 'relaying instance'.

   However, different interfaces can be at different security levels:
   each group of interfaces with the same security level SHOULD be
   serviced by the same GRASP process, except for Limited Security
   Instances Section 3.5.2 which are always single-interface instances
   and MUST NOT perform discovery relaying.

   If a relaying instance receives a Discovery message on a given
   interface for a specific objective that it does not support and for
   which it has not previously cached a Discovery Responder, it MUST
   relay the query by re-issuing a Discovery message as a link-local
   multicast on its other interfaces.

   The relayed discovery message MUST have the same Session ID as the
   incoming discovery message and MUST be tagged with the IP address of
   its original initiator (see Section 3.8.4).  Note that this initiator
   address is only used to allow for disambiguation of the Session ID
   and is never used to address Response packets.

   Since the relay device is unaware of the timeout set by the original
   initiator it SHOULD set a timeout at least equal to GRASP_DEF_TIMEOUT
   milliseconds.




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   The relaying instance MUST decrement the loop count within the
   objective, and MUST NOT relay the Discovery message if the result is
   zero.  Also, it MUST limit the total rate at which it relays
   discovery messages to a reasonable value, in order to mitigate
   possible denial of service attacks.  It MUST cache the Session ID
   value and initiator address of each relayed Discovery message until
   any Discovery Responses have arrived or the discovery process has
   timed out.  To prevent loops, it MUST NOT relay a Discovery message
   which carries a given cached Session ID and initiator address more
   than once.  These precautions avoid discovery loops and mitigate
   potential overload.

   The discovery results received by the relaying instance MUST in turn
   be sent as a Discovery Response message to the Discovery message that
   caused the relay action.

   This relayed discovery mechanism, with caching of the results, should
   be sufficient to support most network bootstrapping scenarios.

3.5.4.5.  Rapid Mode (Discovery/Negotiation binding)

   A Discovery message MAY include a Negotiation Objective option.  This
   allows a rapid mode of negotiation described in Section 3.5.5.  A
   similar mechanism is defined for synchronization in Section 3.5.6.

   Note that rapid mode is currently limited to a single objective for
   simplicity of design and implementation.  A possible future extension
   is to allow multiple objectives in rapid mode for greater efficiency.

3.5.5.  Negotiation Procedures

   A negotiation initiator sends a negotiation request to a counterpart
   ASA, including a specific negotiation objective.  It may request the
   negotiation counterpart to make a specific configuration.
   Alternatively, it may request a certain simulation or forecast result
   by sending a dry run configuration.  The details, including the
   distinction between dry run and an actual configuration change, will
   be defined separately for each type of negotiation objective.

   If no reply message of any kind is received within a reasonable
   timeout (default GRASP_DEF_TIMEOUT milliseconds, Section 3.6), the
   negotiation request MAY be repeated, with a newly generated Session
   ID (Section 3.7).  An exponential backoff SHOULD be used for
   subsequent repetitions.

   If the counterpart can immediately apply the requested configuration,
   it will give an immediate positive (O_ACCEPT) answer (using M_END).
   This will end the negotiation phase immediately.  Otherwise, it will



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   negotiate (using M_NEGOTIATE).  It will reply with a proposed
   alternative configuration that it can apply (typically, a
   configuration that uses fewer resources than requested by the
   negotiation initiator).  This will start a bi-directional negotiation
   (using M_NEGOTIATE) to reach a compromise between the two ASAs.

   The negotiation procedure is ended when one of the negotiation peers
   sends a Negotiation Ending (M_END) message, which contains an accept
   (O_ACCEPT) or decline (O_DECLINE) option and does not need a response
   from the negotiation peer.  Negotiation may also end in failure
   (equivalent to a decline) if a timeout is exceeded or a loop count is
   exceeded.

   A negotiation procedure concerns one objective and one counterpart.
   Both the initiator and the counterpart may take part in simultaneous
   negotiations with various other ASAs, or in simultaneous negotiations
   about different objectives.  Thus, GRASP is expected to be used in a
   multi-threaded mode.  Certain negotiation objectives may have
   restrictions on multi-threading, for example to avoid over-allocating
   resources.

   Some configuration actions, for example wavelength switching in
   optical networks, might take considerable time to execute.  The ASA
   concerned needs to allow for this by design, but GRASP does allow for
   a peer to insert latency in a negotiation process if necessary
   (Section 3.8.9, M_WAIT).

3.5.5.1.  Rapid Mode (Discovery/Negotiation Linkage)

   A Discovery message MAY include a Negotiation Objective option.  In
   this case it is as if the initiator sent the sequence M_DISCOVERY,
   immediately followed by M_REQ_NEG.  This has implications for the
   construction of the GRASP core, as it must carefully pass the
   contents of the Negotiation Objective option to the ASA so that it
   may evaluate the objective directly.  When a Negotiation Objective
   option is present the ASA replies with an M_NEGOTIATE message (or
   M_END with O_ACCEPT if it is immediately satisfied with the
   proposal), rather than with an M_RESPONSE.  However, if the recipient
   node does not support rapid mode, discovery will continue normally.

   It is possible that a Discovery Response will arrive from a responder
   that does not support rapid mode, before such a Negotiation message
   arrives.  In this case, rapid mode will not occur.

   This rapid mode could reduce the interactions between nodes so that a
   higher efficiency could be achieved.  However, a network in which
   some nodes support rapid mode and others do not will have complex
   timing-dependent behaviors.  Therefore, the rapid negotiation



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   function SHOULD be configured off by default and MAY be configured on
   or off by Intent.

3.5.6.  Synchronization and Flooding Procedure

   A synchronization initiator sends a synchronization request to a
   counterpart, including a specific synchronization objective.  The
   counterpart responds with a Synchronization message (Section 3.8.10)
   containing the current value of the requested synchronization
   objective.  No further messages are needed.

   If no reply message of any kind is received within a reasonable
   timeout (default GRASP_DEF_TIMEOUT milliseconds, Section 3.6), the
   synchronization request MAY be repeated, with a newly generated
   Session ID (Section 3.7).  An exponential backoff SHOULD be used for
   subsequent repetitions.

3.5.6.1.  Flooding

   In the case just described, the message exchange is unicast and
   concerns only one synchronization objective.  For large groups of
   nodes requiring the same data, synchronization flooding is available.
   For this, a flooding initiator MAY send an unsolicited Flood
   Synchronization message containing one or more Synchronization
   Objective option(s), if and only if the specification of those
   objectives permits it.  This is sent as a multicast message to the
   ALL_GRASP_NEIGHBOR multicast address (Section 3.6).

   Every network device that supports GRASP always listens to a well-
   known UDP port to capture flooding messages.  Because this port is
   unique in a device, this is a function of the GRASP core.

   To ensure that flooding does not result in a loop, the originator of
   the Flood Synchronization message MUST set the loop count in the
   objectives to a suitable value (the default is GRASP_DEF_LOOPCT).
   Also, a suitable mechanism is needed to avoid excessive multicast
   traffic.  This mechanism MUST be defined as part of the specification
   of the synchronization objective(s) concerned.  It might be a simple
   rate limit or a more complex mechanism such as the Trickle algorithm
   [RFC6206].

   A GRASP device with multiple link-layer interfaces (typically a
   router) MUST support synchronization flooding on all interfaces.  If
   it receives a multicast Flood Synchronization message on a given
   interface, it MUST relay it by re-issuing a Flood Synchronization
   message on its other interfaces.  The relayed message MUST have the
   same Session ID as the incoming message and MUST be tagged with the
   IP address of its original initiator.



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   Link-layer Flooding is supported by GRASP by setting the loop count
   to 1, and sending with a link-local source address.  Floods with
   link-local source addresses and a loop count other than 1 are
   invalid, and such messages MUST be discarded.

   The relaying device MUST decrement the loop count within the first
   objective, and MUST NOT relay the Flood Synchronization message if
   the result is zero.  Also, it MUST limit the total rate at which it
   relays Flood Synchronization messages to a reasonable value, in order
   to mitigate possible denial of service attacks.  It MUST cache the
   Session ID value and initiator address of each relayed Flood
   Synchronization message for a finite time not less than twice
   GRASP_DEF_TIMEOUT milliseconds.  To prevent loops, it MUST NOT relay
   a Flood Synchronization message which carries a given cached Session
   ID and initiator address more than once.  These precautions avoid
   synchronization loops and mitigate potential overload.

   Note that this mechanism is unreliable in the case of sleeping nodes,
   or new nodes that join the network, or nodes that rejoin the network
   after a fault.  An ASA that initiates a flood SHOULD repeat the flood
   at a suitable frequency and SHOULD also act as a synchronization
   responder for the objective(s) concerned.  Thus nodes that require an
   objective subject to flooding can either wait for the next flood or
   request unicast synchronization for that objective.

   The multicast messages for synchronization flooding are subject to
   the security rules in Section 3.5.1.  In practice this means that
   they MUST NOT be transmitted and MUST be ignored on receipt unless
   there is an operational ACP or equivalent strong security in place.
   However, because of the security weakness of link-local multicast
   (Section 5), synchronization objectives that are flooded SHOULD NOT
   contain unencrypted private information and SHOULD be validated by
   the recipient ASA.

3.5.6.2.  Rapid Mode (Discovery/Synchronization Linkage)

   A Discovery message MAY include a Synchronization Objective option.
   In this case the Discovery message also acts as a Request
   Synchronization message to indicate to the Discovery Responder that
   it could directly reply to the Discovery Initiator with a
   Synchronization message Section 3.8.10 with synchronization data for
   rapid processing, if the discovery target supports the corresponding
   synchronization objective.  The design implications are similar to
   those discussed in Section 3.5.5.1.

   It is possible that a Discovery Response will arrive from a responder
   that does not support rapid mode, before such a Synchronization
   message arrives.  In this case, rapid mode will not occur.



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   This rapid mode could reduce the interactions between nodes so that a
   higher efficiency could be achieved.  However, a network in which
   some nodes support rapid mode and others do not will have complex
   timing-dependent behaviors.  Therefore, the rapid synchronization
   function SHOULD be configured off by default and MAY be configured on
   or off by Intent.

3.6.  GRASP Constants

   o  ALL_GRASP_NEIGHBOR

      A link-local scope multicast address used by a GRASP-enabled
      device to discover GRASP-enabled neighbor (i.e., on-link) devices
      . All devices that support GRASP are members of this multicast
      group.

      *  IPv6 multicast address: TBD1

      *  IPv4 multicast address: TBD2

   o  GRASP_LISTEN_PORT (TBD3)

      A well-known UDP user port that every GRASP-enabled network device
      MUST always listen to for link-local multicasts.  Additionally,
      this user port MAY be used to listen for TCP or UDP unicast
      messages in a simple implementation of GRASP (Section 3.5.3).

   o  GRASP_DEF_TIMEOUT (60000 milliseconds)

      The default timeout used to determine that a discovery etc. has
      failed to complete.

   o  GRASP_DEF_LOOPCT (6)

      The default loop count used to determine that a negotiation has
      failed to complete, and to avoid looping messages.

   o  GRASP_DEF_MAX_SIZE (2048)

      The default maximum message size in bytes.

3.7.  Session Identifier (Session ID)

   This is an up to 32-bit opaque value used to distinguish multiple
   sessions between the same two devices.  A new Session ID MUST be
   generated by the initiator for every new Discovery, Flood
   Synchronization or Request message.  All responses and follow-up




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   messages in the same discovery, synchronization or negotiation
   procedure MUST carry the same Session ID.

   The Session ID SHOULD have a very low collision rate locally.  It
   MUST be generated by a pseudo-random algorithm using a locally
   generated seed which is unlikely to be used by any other device in
   the same network [RFC4086].  When allocating a new Session ID, GRASP
   MUST check that the value is not already in use and SHOULD check that
   it has not been used recently, by consulting a cache of current and
   recent sessions.  In the unlikely event of a clash, GRASP MUST
   generate a new value.

   However, there is a finite probability that two nodes might generate
   the same Session ID value.  For that reason, when a Session ID is
   communicated via GRASP, the receiving node MUST tag it with the
   initiator's IP address to allow disambiguation.  In the highly
   unlikely event of two peers opening sessions with the same Session ID
   value, this tag will allow the two sessions to be distinguished.
   Multicast GRASP messages and their responses, which may be relayed
   between links, therefore include a field that carries the initiator's
   global IP address.

   There is a highly unlikely race condition in which two peers start
   simultaneous negotiation sessions with each other using the same
   Session ID value.  Depending on various implementation choices, this
   might lead to the two sessions being confused.  See Section 3.8.6 for
   details of how to avoid this.

3.8.  GRASP Messages

3.8.1.  Message Overview

   This section defines the GRASP message format and message types.
   Message types not listed here are reserved for future use.

   The messages currently defined are:

      Discovery and Discovery Response.

      Request Negotiation, Negotiation, Confirm Waiting and Negotiation
      End.

      Request Synchronization, Synchronization, and Flood
      Synchronization.

      No Operation.





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3.8.2.  GRASP Message Format

   GRASP messages share an identical header format and a variable format
   area for options.  GRASP message headers and options are transmitted
   in Concise Binary Object Representation (CBOR) [RFC7049].  In this
   specification, they are described using CBOR data definition language
   (CDDL) [I-D.greevenbosch-appsawg-cbor-cddl].  Fragmentary CDDL is
   used to describe each item in this section.  A complete and normative
   CDDL specification of GRASP is given in Section 6, including
   constants such as message types.

   Every GRASP message, except the No Operation message, carries a
   Session ID (Section 3.7).  Options are then presented serially in the
   options field.

   In fragmentary CDDL, every GRASP message follows the pattern:

     grasp-message = (message .within message-structure) / noop-message

     message-structure = [MESSAGE_TYPE, session-id, ?initiator,
                          *grasp-option]

     MESSAGE_TYPE = 1..255
     session-id = 0..4294967295 ;up to 32 bits
     grasp-option = any

   The MESSAGE_TYPE indicates the type of the message and thus defines
   the expected options.  Any options received that are not consistent
   with the MESSAGE_TYPE SHOULD be silently discarded.

   The No Operation (noop) message is described in Section 3.8.13.

   The various MESSAGE_TYPE values are defined in Section 6.

   All other message elements are described below and formally defined
   in Section 6.

3.8.3.  Message Size

   GRASP nodes MUST be able to receive messages of at least
   GRASP_DEF_MAX_SIZE bytes.  GRASP nodes MUST NOT send messages longer
   than GRASP_DEF_MAX_SIZE bytes unless a longer size is explicitly
   allowed for the objective concerned.  For example, GRASP negotiation
   itself could be used to agree on a longer message size.

   The message parser used by GRASP should be configured to know about
   the GRASP_DEF_MAX_SIZE, or any larger negotiated message size, so
   that it may defend against overly long messages.



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3.8.4.  Discovery Message

   In fragmentary CDDL, a Discovery message follows the pattern:

     discovery-message = [M_DISCOVERY, session-id, initiator, objective]

   A discovery initiator sends a Discovery message to initiate a
   discovery process for a particular objective option.

   The discovery initiator sends all Discovery messages via UDP to port
   GRASP_LISTEN_PORT at the link-local ALL_GRASP_NEIGHBOR multicast
   address on each link-layer interface in use by GRASP.  It then
   listens for unicast TCP responses on a given port, and stores the
   discovery results (including responding discovery objectives and
   corresponding unicast locators).

   The listening port used for TCP MUST be the same port as used for
   sending the Discovery UDP multicast, on a given interface.  In a low-
   end implementation this MAY be GRASP_LISTEN_PORT.  In a more complex
   implementation, the GRASP discovery mechanism will find, for each
   interface, a dynamic port that it can bind to for both UDP and TCP
   before initiating any discovery.

   The 'initiator' field in the message is a globally unique IP address
   of the initiator, for the sole purpose of disambiguating the Session
   ID in other nodes.  If for some reason the initiator does not have a
   globally unique IP address, it MUST use a link-local address for this
   purpose that is highly likely to be unique, for example using
   [RFC7217].

   A Discovery message MUST include exactly one of the following:

   o  a discovery objective option (Section 3.10.1).  Its loop count
      MUST be set to a suitable value to prevent discovery loops
      (default value is GRASP_DEF_LOOPCT).  If the discovery initiator
      requires only on-link responses, the loop count MUST be set to 1.

   o  a negotiation objective option (Section 3.10.1).  This is used
      both for the purpose of discovery and to indicate to the discovery
      target that it MAY directly reply to the discovery initiatior with
      a Negotiation message for rapid processing, if it could act as the
      corresponding negotiation counterpart.  The sender of such a
      Discovery message MUST initialize a negotiation timer and loop
      count in the same way as a Request Negotiation message
      (Section 3.8.6).

   o  a synchronization objective option (Section 3.10.1).  This is used
      both for the purpose of discovery and to indicate to the discovery



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      target that it MAY directly reply to the discovery initiator with
      a Synchronization message for rapid processing, if it could act as
      the corresponding synchronization counterpart.  Its loop count
      MUST be set to a suitable value to prevent discovery loops
      (default value is GRASP_DEF_LOOPCT).

   Exceptionally, a Discovery message MAY be sent unicast to a peer
   node, which will then proceed exactly as if the message had been
   multicast.

3.8.5.  Discovery Response Message

   In fragmentary CDDL, a Discovery Response message follows the
   pattern:

     response-message = [M_RESPONSE, session-id, initiator, ttl,
                        (+locator-option // divert-option), ?objective)]

     ttl = 0..4294967295 ; in milliseconds

   A node which receives a Discovery message SHOULD send a Discovery
   Response message if and only if it can respond to the discovery.

      It MUST contain the same Session ID and initiator as the Discovery
      message.

      It MUST contain a time-to-live (ttl) for the validity of the
      response, given as a positive integer value in milliseconds.  Zero
      is treated as the default value GRASP_DEF_TIMEOUT (Section 3.6).

      It MAY include a copy of the discovery objective from the
      Discovery message.

   It is sent to the sender of the Discovery message via TCP at the port
   used to send the Discovery message (as explained in Section 3.8.4).

   If the responding node supports the discovery objective of the
   discovery, it MUST include at least one kind of locator option
   (Section 3.9.5) to indicate its own location.  A sequence of multiple
   kinds of locator options (e.g.  IP address option and FQDN option) is
   also valid.

   If the responding node itself does not support the discovery
   objective, but it knows the locator of the discovery objective, then
   it SHOULD respond to the discovery message with a divert option
   (Section 3.9.2) embedding a locator option or a combination of
   multiple kinds of locator options which indicate the locator(s) of
   the discovery objective.



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   More details on the processing of Discovery Responses are given in
   Section 3.5.4.

3.8.6.  Request Messages

   In fragmentary CDDL, Request Negotiation and Request Synchronization
   messages follow the patterns:


   request-negotiation-message = [M_REQ_NEG, session-id, objective]

   request-synchronization-message = [M_REQ_SYN, session-id, objective]


   A negotiation or synchronization requesting node sends the
   appropriate Request message to the unicast address (directly stored
   or resolved from an FQDN or URI) of the negotiation or
   synchronization counterpart, using the appropriate protocol and port
   numbers (selected from the discovery results).

   A Request message MUST include the relevant objective option.  In the
   case of Request Negotiation, the objective option MUST include the
   requested value.

   When an initiator sends a Request Negotiation message, it MUST
   initialize a negotiation timer for the new negotiation thread.  The
   default is GRASP_DEF_TIMEOUT milliseconds.  Unless this timeout is
   modified by a Confirm Waiting message (Section 3.8.9), the initiator
   will consider that the negotiation has failed when the timer expires.

   Similarly, when an initiator sends a Request Synchronization, it
   SHOULD initialize a synchronization timer.  The default is
   GRASP_DEF_TIMEOUT milliseconds.  The initiator will consider that
   synchronization has failed if there is no response before the timer
   expires.

   When an initiator sends a Request message, it MUST initialize the
   loop count of the objective option with a value defined in the
   specification of the option or, if no such value is specified, with
   GRASP_DEF_LOOPCT.

   If a node receives a Request message for an objective for which no
   ASA is currently listening, it MUST immediately close the relevant
   socket to indicate this to the initiator.  This is to avoid
   unnecessary timeouts if, for example, an ASA exits prematurely but
   the GRASP core is listening on its behalf.





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   To avoid the highly unlikely race condition in which two nodes
   simultaneously request sessions with each other using the same
   Session ID (Section 3.7), when a node receives a Request message, it
   MUST verify that the received Session ID is not already locally
   active.  In case of a clash, it MUST discard the Request message, in
   which case the initiator will detect a timeout.

3.8.7.  Negotiation Message

   In fragmentary CDDL, a Negotiation message follows the pattern:

     negotiate-message = [M_NEGOTIATE, session-id, objective]

   A negotiation counterpart sends a Negotiation message in response to
   a Request Negotiation message, a Negotiation message, or a Discovery
   message in Rapid Mode.  A negotiation process MAY include multiple
   steps.

   The Negotiation message MUST include the relevant Negotiation
   Objective option, with its value updated according to progress in the
   negotiation.  The sender MUST decrement the loop count by 1.  If the
   loop count becomes zero the message MUST NOT be sent.  In this case
   the negotiation session has failed and will time out.

3.8.8.  Negotiation End Message

   In fragmentary CDDL, a Negotiation End message follows the pattern:

     end-message = [M_END, session-id, accept-option / decline-option]

   A negotiation counterpart sends an Negotiation End message to close
   the negotiation.  It MUST contain either an accept or a decline
   option, defined in Section 3.9.3 and Section 3.9.4.  It could be sent
   either by the requesting node or the responding node.

3.8.9.  Confirm Waiting Message

   In fragmentary CDDL, a Confirm Waiting message follows the pattern:

     wait-message = [M_WAIT, session-id, waiting-time]
     waiting-time =        0..4294967295 ; in milliseconds

   A responding node sends a Confirm Waiting message to ask the
   requesting node to wait for a further negotiation response.  It might
   be that the local process needs more time or that the negotiation
   depends on another triggered negotiation.  This message MUST NOT
   include any other options.  When received, the waiting time value




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   overwrites and restarts the current negotiation timer
   (Section 3.8.6).

   The responding node SHOULD send a Negotiation, Negotiation End or
   another Confirm Waiting message before the negotiation timer expires.
   If not, the initiator MUST abandon or restart the negotiation
   procedure, to avoid an indefinite wait.

3.8.10.  Synchronization Message

   In fragmentary CDDL, a Synchronization message follows the pattern:

     synch-message = [M_SYNCH, session-id, objective]

   A node which receives a Request Synchronization, or a Discovery
   message in Rapid Mode, sends back a unicast Synchronization message
   with the synchronization data, in the form of a GRASP Option for the
   specific synchronization objective present in the Request
   Synchronization.

3.8.11.  Flood Synchronization Message

   In fragmentary CDDL, a Flood Synchronization message follows the
   pattern:

     flood-message = [M_FLOOD, session-id, initiator, ttl,
                     +[objective, (locator-option / [])]]

     ttl = 0..4294967295 ; in milliseconds

   A node MAY initiate flooding by sending an unsolicited Flood
   Synchronization Message with synchronization data.  This MAY be sent
   to the link-local ALL_GRASP_NEIGHBOR multicast address, in accordance
   with the rules in Section 3.5.6.

      The initiator address is provided, as described for Discovery
      messages (Section 3.8.4), only to disambiguate the Session ID.

      The message MUST contain a time-to-live (ttl) for the validity of
      the contents, given as a positive integer value in milliseconds.
      There is no default; zero indicates an indefinite lifetime.

      The synchronization data are in the form of GRASP Option(s) for
      specific synchronization objective(s).  The loop count(s) MUST be
      set to a suitable value to prevent flood loops (default value is
      GRASP_DEF_LOOPCT).





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      Each objective option MAY be followed by a locator option
      associated with the flooded objective.  In its absence, an empty
      option MUST be included to indicate a null locator.

   A node that receives a Flood Synchronization message MUST cache the
   received objectives for use by local ASAs.  Each cached objective
   MUST be tagged with the locator option sent with it, or with a null
   tag if an empty locator option was sent.  If a subsequent Flood
   Synchronization message carrying the same objective arrives with the
   same tag, the corresponding cached copy of the objective MUST be
   overwritten.  If a subsequent Flood Synchronization message carrying
   the same objective arrives with a different tag, a new cached entry
   MUST be created.

   Note: the purpose of this mechanism is to allow the recipient of
   flooded values to distinguish between different senders of the same
   objective, and if necessary communicate with them using the locator,
   protocol and port included in the locator option.  Many objectives
   will not need this mechanism, so they will be flooded with a null
   locator.

   Cached entries MUST be ignored or deleted after their lifetime
   expires.

3.8.12.  Invalid Message

   In fragmentary CDDL, an Invalid message follows the pattern:

     invalid-message = [M_INVALID, session-id, ?any]

   This message MAY be sent by an implementation in response to an
   incoming message that it considers invalid.  The session-id MUST be
   copied from the incoming message.  The content SHOULD be diagnostic
   information such as a partial copy of the invalid message.  An
   M_INVALID message MAY be silently ignored by a recipient.  However,
   it could be used in support of extensibility, since it indicates that
   the remote node does not support a new or obsolete message or option

   An M_INVALID message MUST NOT be sent in response to an M_INVALID
   message.

3.8.13.  No Operation Message

   In fragmentary CDDL, a No Operation message follows the pattern:

     noop-message = [M_NOOP]





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   This message MAY be sent by an implementation that for practical
   reasons needs to activate a socket.  It MUST be silently ignored by a
   recipient.

3.9.  GRASP Options

   This section defines the GRASP options for the negotiation and
   synchronization protocol signaling.  Additional options may be
   defined in the future.

3.9.1.  Format of GRASP Options

   GRASP options are CBOR objects that MUST start with an unsigned
   integer identifying the specific option type carried in this option.
   These option types are formally defined in Section 6.  Apart from
   that the only format requirement is that each option MUST be a well-
   formed CBOR object.  In general a CBOR array format is RECOMMENDED to
   limit overhead.

   GRASP options are usually scoped by using encapsulation.  However,
   this is not a requirement

3.9.2.  Divert Option

   The Divert option is used to redirect a GRASP request to another
   node, which may be more appropriate for the intended negotiation or
   synchronization.  It may redirect to an entity that is known as a
   specific negotiation or synchronization counterpart (on-link or off-
   link) or a default gateway.  The divert option MUST only be
   encapsulated in Discovery Response messages.  If found elsewhere, it
   SHOULD be silently ignored.

   A discovery initiator MAY ignore a Divert option if it only requires
   direct discovery responses.

   In fragmentary CDDL, the Divert option follows the pattern:

     divert-option = [O_DIVERT, +locator-option]

   The embedded Locator Option(s) (Section 3.9.5) point to diverted
   destination target(s) in response to a Discovery message.

3.9.3.  Accept Option

   The accept option is used to indicate to the negotiation counterpart
   that the proposed negotiation content is accepted.





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   The accept option MUST only be encapsulated in Negotiation End
   messages.  If found elsewhere, it SHOULD be silently ignored.

   In fragmentary CDDL, the Accept option follows the pattern:

     accept-option = [O_ACCEPT]

3.9.4.  Decline Option

   The decline option is used to indicate to the negotiation counterpart
   the proposed negotiation content is declined and end the negotiation
   process.

   The decline option MUST only be encapsulated in Negotiation End
   messages.  If found elsewhere, it SHOULD be silently ignored.

   In fragmentary CDDL, the Decline option follows the pattern:

     decline-option = [O_DECLINE, ?reason]
     reason = text  ;optional error message

   Note: there are scenarios where a negotiation counterpart wants to
   decline the proposed negotiation content and continue the negotiation
   process.  For these scenarios, the negotiation counterpart SHOULD use
   a Negotiate message, with either an objective option that contains a
   data field set to indicate a meaningless initial value, or a specific
   objective option that provides further conditions for convergence.

3.9.5.  Locator Options

   These locator options are used to present reachability information
   for an ASA, a device or an interface.  They are Locator IPv6 Address
   Option, Locator IPv4 Address Option, Locator FQDN (Fully Qualified
   Domain Name) Option and URI (Uniform Resource Identifier) Option.

   Since ASAs will normally run as independent user programs, locator
   options need to indicate the network layer locator plus the transport
   protocol and port number for reaching the target.  For this reason,
   the Locator Options for IP addresses and FQDNs include this
   information explicitly.  In the case of the URI Option, this
   information can be encoded in the URI itself.

   Note: It is assumed that all locators are in scope throughout the
   GRASP domain.  GRASP is not intended to work across disjoint
   addressing or naming realms.






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3.9.5.1.  Locator IPv6 address option

   In fragmentary CDDL, the IPv6 address option follows the pattern:

     ipv6-locator-option = [O_IPv6_LOCATOR, ipv6-address,
                            transport-proto, port-number]
     ipv6-address = bytes .size 16

     transport-proto = IPPROTO_TCP / IPPROTO_UDP
     IPPROTO_TCP = 6
     IPPROTO_UDP = 17
     port-number = 0..65535

   The content of this option is a binary IPv6 address followed by the
   protocol number and port number to be used.

   Note 1: The IPv6 address MUST normally have global scope.
   Exceptionally, during initialisation, a link-local address MAY be
   used for specific objectives only (Section 3.5.2).  In this case the
   corresponding Discovery Response message MUST be sent via the
   interface to which the link-local address applies.

   Note 2: A link-local IPv6 address MUST NOT be used when this option
   is included in a Divert option.

3.9.5.2.  Locator IPv4 address option

   In fragmentary CDDL, the IPv4 address option follows the pattern:

     ipv4-locator-option = [O_IPv4_LOCATOR, ipv4-address,
                            transport-proto, port-number]
     ipv4-address = bytes .size 4

   The content of this option is a binary IPv4 address followed by the
   protocol number and port number to be used.

   Note: If an operator has internal network address translation for
   IPv4, this option MUST NOT be used within the Divert option.

3.9.5.3.  Locator FQDN option

   In fragmentary CDDL, the FQDN option follows the pattern:

     fqdn-locator-option = [O_FQDN_LOCATOR, text,
                            transport-proto, port-number]

   The content of this option is the Fully Qualified Domain Name of the
   target followed by the protocol number and port number to be used.



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   Note 1: Any FQDN which might not be valid throughout the network in
   question, such as a Multicast DNS name [RFC6762], MUST NOT be used
   when this option is used within the Divert option.

   Note 2: Normal GRASP operations are not expected to use this option.
   It is intended for special purposes such as discovering external
   services.

3.9.5.4.  Locator URI option

   In fragmentary CDDL, the URI option follows the pattern:

     uri-locator = [O_URI_LOCATOR, text]

   The content of this option is the Uniform Resource Identifier of the
   target [RFC3986].

   Note 1: Any URI which might not be valid throughout the network in
   question, such as one based on a Multicast DNS name [RFC6762], MUST
   NOT be used when this option is used within the Divert option.

   Note 2: Normal GRASP operations are not expected to use this option.
   It is intended for special purposes such as discovering external
   services.

3.10.  Objective Options

3.10.1.  Format of Objective Options

   An objective option is used to identify objectives for the purposes
   of discovery, negotiation or synchronization.  All objectives MUST be
   in the following format, described in fragmentary CDDL:

     objective = [objective-name, objective-flags, loop-count, ?any]

     objective-name = text
     loop-count = 0..255

   All objectives are identified by a unique name which is a case-
   sensitive UTF-8 string.

   The names of generic objectives MUST NOT include a colon (":") and
   MUST be registered with IANA (Section 7).

   The names of privately defined objectives MUST include at least one
   colon (":").  The string preceding the last colon in the name MUST be
   globally unique and in some way identify the entity or person




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   defining the objective.  The following three methods MAY be used to
   create such a globally unique string:

   1.  The unique string is a decimal number representing a registered
       32 bit Private Enterprise Number (PEN) [I-D.liang-iana-pen] that
       uniquely identifies the enterprise defining the objective.

   2.  The unique string is a fully qualified domain name that uniquely
       identifies the entity or person defining the objective.

   3.  The unique string is an email address that uniquely identifies
       the entity or person defining the objective.

   The GRASP protocol treats the objective name as an opaque string.
   For example, "EX1", "411:EX1", "example.com:EX1", "example.org:EX1
   and "user@example.org:EX1" would be five different objectives.

   The 'objective-flags' field is described below.

   The 'loop-count' field is used for terminating negotiation as
   described in Section 3.8.7.  It is also used for terminating
   discovery as described in Section 3.5.4, and for terminating flooding
   as described in Section 3.5.6.1.

   The 'any' field is to express the actual value of a negotiation or
   synchronization objective.  Its format is defined in the
   specification of the objective and may be a single value or a data
   structure of any kind.  It is optional because it is optional in a
   Discovery or Discovery Response message.

3.10.2.  Objective flags

   An objective may be relevant for discovery only, for discovery and
   negotiation, or for discovery and synchronization.  This is expressed
   in the objective by logical flag bits:

     objective-flags = uint .bits objective-flag
     objective-flag = &(
     F_DISC: 0    ; valid for discovery
     F_NEG: 1     ; valid for negotiation
     F_SYNCH: 2   ; valid for synchronization
     F_NEG_DRY: 3 ; negotiation is dry-run
     )

   These bits are independent and may be combined appropriately, e.g.
   (F_DISC and F_SYNCH) or (F_DISC and F_NEG) or (F_DISC and F_NEG and
   F_NEG_DRY).




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   Note that for a given negotiation session, an objective must be
   either used for negotiation, or for dry-run negotiation.  Mixing the
   two modes in a single negotiation is not possible.

3.10.3.  General Considerations for Objective Options

   As mentioned above, Objective Options MUST be assigned a unique name.
   As long as privately defined Objective Options obey the rules above,
   this document does not restrict their choice of name, but the entity
   or person concerned SHOULD publish the names in use.

   All Objective Options MUST respect the CBOR patterns defined above as
   "objective" and MUST replace the "any" field with a valid CBOR data
   definition for the relevant use case and application.

   An Objective Option that contains no additional fields beyond its
   "loop-count" can only be a discovery objective and MUST only be used
   in Discovery and Discovery Response messages.

   The Negotiation Objective Options contain negotiation objectives,
   which vary according to different functions/services.  They MUST be
   carried by Discovery, Request Negotiation or Negotiation messages
   only.  The negotiation initiator MUST set the initial "loop-count" to
   a value specified in the specification of the objective or, if no
   such value is specified, to GRASP_DEF_LOOPCT.

   For most scenarios, there should be initial values in the negotiation
   requests.  Consequently, the Negotiation Objective options MUST
   always be completely presented in a Request Negotiation message, or
   in a Discovery message in rapid mode.  If there is no initial value,
   the bits in the value field SHOULD all be set to indicate a
   meaningless value, unless this is inappropriate for the specific
   negotiation objective.

   Synchronization Objective Options are similar, but MUST be carried by
   Discovery, Discovery Response, Request Synchronization, or Flood
   Synchronization messages only.  They include value fields only in
   Synchronization or Flood Synchronization messages.

3.10.4.  Organizing of Objective Options

   Generic objective options MUST be specified in documents available to
   the public and SHOULD be designed to use either the negotiation or
   the synchronization mechanism described above.

   As noted earlier, one negotiation objective is handled by each GRASP
   negotiation thread.  Therefore, a negotiation objective, which is
   based on a specific function or action, SHOULD be organized as a



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   single GRASP option.  It is NOT RECOMMENDED to organize multiple
   negotiation objectives into a single option, nor to split a single
   function or action into multiple negotiation objectives.

   It is important to understand that GRASP negotiation does not support
   transactional integrity.  If transactional integrity is needed for a
   specific objective, this must be ensured by the ASA.  For example, an
   ASA might need to ensure that it only participates in one negotiation
   thread at the same time.  Such an ASA would need to stop listening
   for incoming negotiation requests before generating an outgoing
   negotiation request.

   A synchronization objective SHOULD be organized as a single GRASP
   option.

   Some objectives will support more than one operational mode.  An
   example is a negotiation objective with both a "dry run" mode (where
   the negotiation is to find out whether the other end can in fact make
   the requested change without problems) and a "live" mode.  Such modes
   will be defined in the specification of such an objective.  These
   objectives SHOULD include flags indicating the applicable mode(s).

   An objective may have multiple parameters.  Parameters can be
   categorized into two classes: the obligatory ones presented as fixed
   fields; and the optional ones presented in CBOR sub-options or some
   other form of data structure embedded in CBOR.  The format might be
   inherited from an existing management or configuration protocol, the
   objective option acting as a carrier for that format.  The data
   structure might be defined in a formal language, but that is a matter
   for the specifications of individual objectives.  There are many
   candidates, according to the context, such as ABNF, RBNF, XML Schema,
   possibly YANG, etc.  The GRASP protocol itself is agnostic on these
   questions.

   It is NOT RECOMMENDED to split parameters in a single objective into
   multiple options, unless they have different response periods.  An
   exception scenario may also be described by split objectives.

   All objectives MUST support GRASP discovery.  However, as mentioned
   in Section 3.3, it is acceptable for an ASA to use an alternative
   method of discovery.

   Normally, a GRASP objective will refer to specific technical
   parameters as explained in Section 3.1.  However, it is acceptable to
   define an abstract objective for the purpose of managing or
   coordinating ASAs.  It is also acceptable to define a special-purpose
   objective for purposes such as trust bootstrapping or formation of
   the ACP.



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   To guarantee convergence, a limited number of rounds or a timeout is
   needed for each negotiation objective.  Therefore, the definition of
   each negotiation objective SHOULD clearly specify this, for example a
   default loop count and timeout, so that the negotiation can always be
   terminated properly.  If not, the GRASP defaults will apply.

   There must be a well-defined procedure for concluding that a
   negotiation cannot succeed, and if so deciding what happens next
   (e.g., deadlock resolution, tie-breaking, or revert to best-effort
   service).  This MUST be specified for individual negotiation
   objectives.

3.10.5.  Experimental and Example Objective Options

   The names "EX0" through "EX9" have been reserved for experimental
   options.  Multiple names have been assigned because a single
   experiment may use multiple options simultaneously.  These
   experimental options are highly likely to have different meanings
   when used for different experiments.  Therefore, they SHOULD NOT be
   used without an explicit human decision and SHOULD NOT be used in
   unmanaged networks such as home networks.

   These names are also RECOMMENDED for use in documentation examples.

4.  Implementation Status [RFC Editor: please remove]

   Two prototype implementations of GRASP have been made.

4.1.  BUPT C++ Implementation

   o  Name: BaseNegotiator.cpp, msg.cpp, Client.cpp, Server.cpp

   o  Description: C++ implementation of GRASP core and API

   o  Maturity: Prototype code, interoperable between Ubuntu.

   o  Coverage: Corresponds to draft-carpenter-anima-gdn-protocol-03.
      Since it was implemented based on the old version draft, the most
      significant limitations comparing to current protocol design
      include:

      *  Not support CBOR

      *  Not support Flooding

      *  Not support loop avoidance

      *  only coded for IPv6, any IPv4 is accidental



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   o  Licensing: Huawei License.

   o  Experience: https://github.com/liubingpang/IETF-Anima-Signaling-
      Protocol/blob/master/README.md

   o  Contact: https://github.com/liubingpang/IETF-Anima-Signaling-
      Protocol

4.2.  Python Implementation

   o  Name: graspy

   o  Description: Python 3 implementation of GRASP core and API.

   o  Maturity: Prototype code, interoperable between Windows 7 and
      Linux.

   o  Coverage: Corresponds to draft-ietf-anima-grasp-08.  Limitations
      include:

      *  insecure: uses a dummy ACP module and does not implement TLS

      *  only coded for IPv6, any IPv4 is accidental

      *  FQDN and URI locators incompletely supported

      *  no code for rapid mode

      *  relay code is lazy (no rate control)

      *  all unicast transactions use TCP (no unicast UDP).
         Experimental code for unicast UDP proved to be complex and
         brittle.

      *  optional Objective option in Response messages not implemented

      *  workarounds for defects in Python socket module and Windows
         socket peculiarities

   o  Licensing: Simplified BSD

   o  Experience: https://www.cs.auckland.ac.nz/~brian/graspy/graspy.pdf

   o  Contact: https://www.cs.auckland.ac.nz/~brian/graspy/







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5.  Security Considerations

   It is obvious that a successful attack on negotiation-enabled nodes
   would be extremely harmful, as such nodes might end up with a
   completely undesirable configuration that would also adversely affect
   their peers.  GRASP nodes and messages therefore require full
   protection.

   - Authentication

      A cryptographically authenticated identity for each device is
      needed in an autonomic network.  It is not safe to assume that a
      large network is physically secured against interference or that
      all personnel are trustworthy.  Each autonomic node MUST be
      capable of proving its identity and authenticating its messages.
      GRASP relies on a separate external certificate-based security
      mechanism to support authentication, data integrity protection,
      and anti-replay protection.

      Since GRASP is intended to be deployed in a single administrative
      domain operating its own trust anchor and CA, there is no need for
      a trusted public third party.  In a network requiring "air gap"
      security, such a dependency would be unacceptable.

      If GRASP is used temporarily without an external security
      mechanism, for example during system bootstrap (Section 3.5.1),
      the Session ID (Section 3.7) will act as a nonce to provide
      limited protection against third parties injecting responses.  A
      full analysis of the secure bootstrap process is out of scope for
      the present document.

   - Authorization and Roles

      The GRASP protocol is agnostic about the role of individual ASAs
      and about which objectives a particular ASA is authorized to
      support.  An implementation might support precautions such as
      allowing only one ASA in a given node to modify a given objective,
      but this may not be appropriate in all cases.  For example, it
      might be operationally useful to allow an old and a new version of
      the same ASA to run simultaneously during an overlap period.
      These questions are out of scope for the present specification.

   - Privacy and confidentiality

      Generally speaking, no personal information is expected to be
      involved in the signaling protocol, so there should be no direct
      impact on personal privacy.  Nevertheless, traffic flow paths,
      VPNs, etc. could be negotiated, which could be of interest for



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      traffic analysis.  Also, operators generally want to conceal
      details of their network topology and traffic density from
      outsiders.  Therefore, since insider attacks cannot be excluded in
      a large network, the security mechanism for the protocol MUST
      provide message confidentiality.  This is why Section 3.5.1
      requires either an ACP or an alternative security mechanism.

   - Link-local multicast security

      GRASP has no reasonable alternative to using link-local multicast
      for Discovery or Flood Synchronization messages and these messages
      are sent in clear and with no authentication.  They are therefore
      available to on-link eavesdroppers, and could be forged by on-link
      attackers.  In the case of Discovery, the Discovery Responses are
      unicast and will therefore be protected (Section 3.5.1), and an
      untrusted forger will not be able to receive responses.  In the
      case of Flood Synchronization, an on-link eavesdropper will be
      able to receive the flooded objectives but there is no response
      message to consider.  Some precautions for Flood Synchronization
      messages are suggested in Section 3.5.6.1.

   - DoS Attack Protection

      GRASP discovery partly relies on insecure link-local multicast.
      Since routers participating in GRASP sometimes relay discovery
      messages from one link to another, this could be a vector for
      denial of service attacks.  Some mitigations are specified in
      Section 3.5.4.  However, malicious code installed inside the
      Autonomic Control Plane could always launch DoS attacks consisting
      of spurious discovery messages, or of spurious discovery
      responses.  Additionally, it is of great importance that firewalls
      prevent any GRASP messages from entering the domain from an
      untrusted source.

   - Security during bootstrap and discovery

      A node cannot authenticate GRASP traffic from other nodes until it
      has identified the trust anchor and can validate certificates for
      other nodes.  Also, until it has succesfully enrolled
      [I-D.ietf-anima-bootstrapping-keyinfra] it cannot assume that
      other nodes are able to authenticate its own traffic.  Therefore,
      GRASP discovery during the bootstrap phase for a new device will
      inevitably be insecure and GRASP synchronization and negotiation
      will be impossible until enrollment is complete.  Further details
      are given in Section 3.5.2.

   - Security of discovered locators




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      When GRASP discovery returns an IP address, it MUST be that of a
      node within the secure environment (Section 3.5.1).  If it returns
      an FQDN or a URI, the ASA that receives it MUST NOT assume that
      the target of the locator is within the secure environment.

6.  CDDL Specification of GRASP

  <CODE BEGINS>
  grasp-message = (message .within message-structure) / noop-message

  message-structure = [MESSAGE_TYPE, session-id, ?initiator,
                       *grasp-option]

  MESSAGE_TYPE = 0..255
  session-id = 0..4294967295 ;up to 32 bits
  grasp-option = any

  message /= discovery-message
  discovery-message = [M_DISCOVERY, session-id, initiator, objective]

  message /= response-message ;response to Discovery
  response-message = [M_RESPONSE, session-id, initiator, ttl,
                     (+locator-option // divert-option), ?objective]

  message /= synch-message ;response to Synchronization request
  synch-message = [M_SYNCH, session-id, objective]

  message /= flood-message
  flood-message = [M_FLOOD, session-id, initiator, ttl,
                  +[objective, (locator-option / [])]]

  message /= request-negotiation-message
  request-negotiation-message = [M_REQ_NEG, session-id, objective]

  message /= request-synchronization-message
  request-synchronization-message = [M_REQ_SYN, session-id, objective]

  message /= negotiation-message
  negotiation-message = [M_NEGOTIATE, session-id, objective]

  message /= end-message
  end-message = [M_END, session-id, accept-option / decline-option ]

  message /= wait-message
  wait-message = [M_WAIT, session-id, waiting-time]

  message /= invalid-message
  invalid-message = [M_INVALID, session-id, ?any]



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  noop-message = [M_NOOP]

  divert-option = [O_DIVERT, +locator-option]

  accept-option = [O_ACCEPT]

  decline-option = [O_DECLINE, ?reason]
  reason = text  ;optional error message

  waiting-time = 0..4294967295 ; in milliseconds
  ttl = 0..4294967295 ; in milliseconds

  locator-option /= [O_IPv4_LOCATOR, ipv4-address,
                     transport-proto, port-number]
  ipv4-address = bytes .size 4

  locator-option /= [O_IPv6_LOCATOR, ipv6-address,
                     transport-proto, port-number]
  ipv6-address = bytes .size 16

  locator-option /= [O_FQDN_LOCATOR, text, transport-proto, port-number]

  transport-proto = IPPROTO_TCP / IPPROTO_UDP
  IPPROTO_TCP = 6
  IPPROTO_UDP = 17
  port-number = 0..65535

  locator-option /= [O_URI_LOCATOR, text]

  initiator = ipv4-address / ipv6-address

  objective-flags = uint .bits objective-flag

  objective-flag = &(
    F_DISC: 0    ; valid for discovery
    F_NEG: 1     ; valid for negotiation
    F_SYNCH: 2   ; valid for synchronization
    F_NEG_DRY: 3 ; negotiation is dry-run
  )

  objective = [objective-name, objective-flags, loop-count, ?any]

  objective-name = text ;see specification for uniqueness rules

  loop-count = 0..255

  ; Constants for message types and option types




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  M_NOOP = 0
  M_DISCOVERY = 1
  M_RESPONSE = 2
  M_REQ_NEG = 3
  M_REQ_SYN = 4
  M_NEGOTIATE = 5
  M_END = 6
  M_WAIT = 7
  M_SYNCH = 8
  M_FLOOD = 9
  M_INVALID = 99

  O_DIVERT = 100
  O_ACCEPT = 101
  O_DECLINE = 102
  O_IPv6_LOCATOR = 103
  O_IPv4_LOCATOR = 104
  O_FQDN_LOCATOR = 105
  O_URI_LOCATOR = 106
  <CODE ENDS>

7.  IANA Considerations

   This document defines the Generic Autonomic Signaling Protocol
   (GRASP).

   Section 3.6 explains the following link-local multicast addresses,
   which IANA is requested to assign for use by GRASP:

   ALL_GRASP_NEIGHBOR multicast address  (IPv6): (TBD1).  Assigned in
      the IPv6 Link-Local Scope Multicast Addresses registry.

   ALL_GRASP_NEIGHBOR multicast address  (IPv4): (TBD2).  Assigned in
      the IPv4 Multicast Local Network Control Block.

   Section 3.6 explains the following User Port, which IANA is requested
   to assign for use by GRASP for both UDP and TCP:

   GRASP_LISTEN_PORT: (TBD3)
   Service Name: Generic Autonomic Signaling Protocol (GRASP)
   Transport Protocols: UDP, TCP
   Assignee: iesg@ietf.org
   Contact: chair@ietf.org
   Description: See Section 3.6
   Reference: RFC XXXX (this document)






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   The IANA is requested to create a GRASP Parameter Registry including
   two registry tables.  These are the GRASP Messages and Options
   Table and the GRASP Objective Names Table.

   GRASP Messages and Options Table.  The values in this table are names
   paired with decimal integers.  Future values MUST be assigned using
   the Standards Action policy defined by [RFC5226].  The following
   initial values are assigned by this document:

   M_NOOP = 0
   M_DISCOVERY = 1
   M_RESPONSE = 2
   M_REQ_NEG = 3
   M_REQ_SYN = 4
   M_NEGOTIATE = 5
   M_END = 6
   M_WAIT = 7
   M_SYNCH = 8
   M_FLOOD = 9
   M_INVALID = 99

   O_DIVERT = 100
   O_ACCEPT = 101
   O_DECLINE = 102
   O_IPv6_LOCATOR = 103
   O_IPv4_LOCATOR = 104
   O_FQDN_LOCATOR = 105
   O_URI_LOCATOR = 106

   GRASP Objective Names Table.  The values in this table are UTF-8
   strings.  Future values MUST be assigned using the Specification
   Required policy defined by [RFC5226].  The following initial values
   are assigned by this document:

    EX0
    EX1
    EX2
    EX3
    EX4
    EX5
    EX6
    EX7
    EX8
    EX9







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8.  Acknowledgements

   A major contribution to the original version of this document was
   made by Sheng Jiang.  Significant review inputs were received from
   Joel Halpern, Toerless Eckert and Michael Richardson.

   Valuable comments were received from Michael Behringer, Jeferson
   Campos Nobre, Laurent Ciavaglia, Zongpeng Du, Yu Fu, Zhenbin Li,
   Dimitri Papadimitriou, Pierre Peloso, Reshad Rahman, Markus Stenberg,
   Rene Struik, Dacheng Zhang, and other participants in the NMRG
   research group and the ANIMA working group.

9.  References

9.1.  Normative References

   [I-D.greevenbosch-appsawg-cbor-cddl]
              Vigano, C. and H. Birkholz, "CBOR data definition language
              (CDDL): a notational convention to express CBOR data
              structures", draft-greevenbosch-appsawg-cbor-cddl-09 (work
              in progress), September 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <http://www.rfc-editor.org/info/rfc4086>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.




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   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <http://www.rfc-editor.org/info/rfc7049>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <http://www.rfc-editor.org/info/rfc7217>.

9.2.  Informative References

   [I-D.chaparadza-intarea-igcp]
              Behringer, M., Chaparadza, R., Petre, R., Li, X., and H.
              Mahkonen, "IP based Generic Control Protocol (IGCP)",
              draft-chaparadza-intarea-igcp-00 (work in progress), July
              2011.

   [I-D.ietf-anima-autonomic-control-plane]
              Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
              Control Plane", draft-ietf-anima-autonomic-control-
              plane-04 (work in progress), October 2016.

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
              S., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-04 (work in progress), October 2016.

   [I-D.ietf-anima-reference-model]
              Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
              Pierre, P., Liu, B., Nobre, J., and J. Strassner, "A
              Reference Model for Autonomic Networking", draft-ietf-
              anima-reference-model-02 (work in progress), July 2016.

   [I-D.ietf-anima-stable-connectivity]
              Eckert, T. and M. Behringer, "Using Autonomic Control
              Plane for Stable Connectivity of Network OAM", draft-ietf-
              anima-stable-connectivity-01 (work in progress), July
              2016.







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   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-18 (work in
              progress), October 2016.

   [I-D.liang-iana-pen]
              Liang, P., Melnikov, A., and D. Conrad, "Private
              Enterprise Number (PEN) practices and Internet Assigned
              Numbers Authority (IANA) registration considerations",
              draft-liang-iana-pen-06 (work in progress), July 2015.

   [I-D.liu-anima-grasp-api]
              Carpenter, B., Liu, B., Wang, W., and X. Gong, "Generic
              Autonomic Signaling Protocol Application Program Interface
              (GRASP API)", draft-liu-anima-grasp-api-02 (work in
              progress), September 2016.

   [I-D.stenberg-anima-adncp]
              Stenberg, M., "Autonomic Distributed Node Consensus
              Protocol", draft-stenberg-anima-adncp-00 (work in
              progress), March 2015.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <http://www.rfc-editor.org/info/rfc2205>.

   [RFC2334]  Luciani, J., Armitage, G., Halpern, J., and N. Doraswamy,
              "Server Cache Synchronization Protocol (SCSP)", RFC 2334,
              DOI 10.17487/RFC2334, April 1998,
              <http://www.rfc-editor.org/info/rfc2334>.

   [RFC2608]  Guttman, E., Perkins, C., Veizades, J., and M. Day,
              "Service Location Protocol, Version 2", RFC 2608,
              DOI 10.17487/RFC2608, June 1999,
              <http://www.rfc-editor.org/info/rfc2608>.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, DOI 10.17487/RFC2865, June 2000,
              <http://www.rfc-editor.org/info/rfc2865>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.





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   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3416]  Presuhn, R., Ed., "Version 2 of the Protocol Operations
              for the Simple Network Management Protocol (SNMP)",
              STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
              <http://www.rfc-editor.org/info/rfc3416>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5971]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
              Signalling Transport", RFC 5971, DOI 10.17487/RFC5971,
              October 2010, <http://www.rfc-editor.org/info/rfc5971>.

   [RFC6206]  Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
              "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206,
              March 2011, <http://www.rfc-editor.org/info/rfc6206>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,
              <http://www.rfc-editor.org/info/rfc6733>.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013,
              <http://www.rfc-editor.org/info/rfc6762>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
              <http://www.rfc-editor.org/info/rfc6763>.






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   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <http://www.rfc-editor.org/info/rfc6887>.

   [RFC7558]  Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
              "Requirements for Scalable DNS-Based Service Discovery
              (DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558,
              DOI 10.17487/RFC7558, July 2015,
              <http://www.rfc-editor.org/info/rfc7558>.

   [RFC7575]  Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking: Definitions and Design Goals", RFC 7575,
              DOI 10.17487/RFC7575, June 2015,
              <http://www.rfc-editor.org/info/rfc7575>.

   [RFC7576]  Jiang, S., Carpenter, B., and M. Behringer, "General Gap
              Analysis for Autonomic Networking", RFC 7576,
              DOI 10.17487/RFC7576, June 2015,
              <http://www.rfc-editor.org/info/rfc7576>.

   [RFC7787]  Stenberg, M. and S. Barth, "Distributed Node Consensus
              Protocol", RFC 7787, DOI 10.17487/RFC7787, April 2016,
              <http://www.rfc-editor.org/info/rfc7787>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <http://www.rfc-editor.org/info/rfc7788>.

Appendix A.  Open Issues [RFC Editor: Please remove if empty]

   o  63.  Placeholder

Appendix B.  Closed Issues [RFC Editor: Please remove]

   o  1.  UDP vs TCP: For now, this specification suggests UDP and TCP
      as message transport mechanisms.  This is not clarified yet.  UDP
      is good for short conversations, is necessary for multicast
      discovery, and generally fits the discovery and divert scenarios
      well.  However, it will cause problems with large messages.  TCP
      is good for stable and long sessions, with a little bit of time
      consumption during the session establishment stage.  If messages
      exceed a reasonable MTU, a TCP mode will be required in any case.
      This question may be affected by the security discussion.

      RESOLVED by specifying UDP for short message and TCP for longer
      one.



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   o  2.  DTLS or TLS vs built-in security mechanism.  For now, this
      specification has chosen a PKI based built-in security mechanism
      based on asymmetric cryptography.  However, (D)TLS might be chosen
      as security solution to avoid duplication of effort.  It also
      allows essentially similar security for short messages over UDP
      and longer ones over TCP.  The implementation trade-offs are
      different.  The current approach requires expensive asymmetric
      cryptographic calculations for every message.  (D)TLS has startup
      overheads but cheaper crypto per message.  DTLS is less mature
      than TLS.

      RESOLVED by specifying external security (ACP or (D)TLS).

   o  The following open issues applied only if the original security
      model was retained:

      *  2.1.  For replay protection, GRASP currently requires every
         participant to have an NTP-synchronized clock.  Is this OK for
         low-end devices, and how does it work during device
         bootstrapping?  We could take the Timestamp out of signature
         option, to become an independent and OPTIONAL (or RECOMMENDED)
         option.

      *  2.2.  The Signature Option states that this option could be any
         place in a message.  Wouldn't it be better to specify a
         position (such as the end)?  That would be much simpler to
         implement.

      RESOLVED by changing security model.

   o  3.  DoS Attack Protection needs work.

      RESOLVED by adding text.

   o  4.  Should we consider preferring a text-based approach to
      discovery (after the initial discovery needed for bootstrapping)?
      This could be a complementary mechanism for multicast based
      discovery, especially for a very large autonomic network.
      Centralized registration could be automatically deployed
      incrementally.  At the very first stage, the repository could be
      empty; then it could be filled in by the objectives discovered by
      different devices (for example using Dynamic DNS Update).  The
      more records are stored in the repository, the less the multicast-
      based discovery is needed.  However, if we adopt such a mechanism,
      there would be challenges: stateful solution, and security.

      RESOLVED for now by adding optional use of DNS-SD by ASAs.
      Subsequently removed by editors as irrelevant to GRASP istelf.



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   o  5.  Need to expand description of the minimum requirements for the
      specification of an individual discovery, synchronization or
      negotiation objective.

      RESOLVED for now by extra wording.

   o  6.  Use case and protocol walkthrough.  A description of how a
      node starts up, performs discovery, and conducts negotiation and
      synchronisation for a sample use case would help readers to
      understand the applicability of this specification.  Maybe it
      should be an artificial use case or maybe a simple real one, based
      on a conceptual API.  However, the authors have not yet decided
      whether to have a separate document or have it in the protocol
      document.

      RESOLVED: recommend a separate document.

   o  7.  Cross-check against other ANIMA WG documents for consistency
      and gaps.

      RESOLVED: Satisfied by WGLC.

   o  8.  Consideration of ADNCP proposal.

      RESOLVED by adding optional use of DNCP for flooding-type
      synchronization.

   o  9.  Clarify how a GDNP instance knows whether it is running inside
      the ACP.  (Sheng)

      RESOLVED by improved text.

   o  10.  Clarify how a non-ACP GDNP instance initiates (D)TLS.
      (Sheng)

      RESOLVED by improved text and declaring DTLS out of scope for this
      draft.

   o  11.  Clarify how UDP/TCP choice is made.  (Sheng) [Like DNS? -
      Brian]

      RESOLVED by improved text.

   o  12.  Justify that IP address within ACP or (D)TLS environment is
      sufficient to prove AN identity; or explain how Device Identity
      Option is used.  (Sheng)





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      RESOLVED for now: we assume that all ASAs in a device are trusted
      as soon as the device is trusted, so they share credentials.  In
      that case the Device Identity Option is useless.  This needs to be
      reviewed later.

   o  13.  Emphasise that negotiation/synchronization are independent
      from discovery, although the rapid discovery mode includes the
      first step of a negotiation/synchronization.  (Sheng)

      RESOLVED by improved text.

   o  14.  Do we need an unsolicited flooding mechanism for discovery
      (for discovery results that everyone needs), to reduce scaling
      impact of flooding discovery messages?  (Toerless)

      RESOLVED: Yes, added to requirements and solution.

   o  15.  Do we need flag bits in Objective Options to distinguish
      distinguish Synchronization and Negotiation "Request" or rapid
      mode "Discovery" messages?  (Bing)

      RESOLVED: yes, work on the API showed that these flags are
      essential.

   o  16.  (Related to issue 14).  Should we revive the "unsolicited
      Response" for flooding synchronisation data?  This has to be done
      carefully due to the well-known issues with flooding, but it could
      be useful, e.g. for Intent distribution, where DNCP doesn't seem
      applicable.

      RESOLVED: Yes, see #14.

   o  17.  Ensure that the discovery mechanism is completely proof
      against loops and protected against duplicate responses.

      RESOLVED: Added loop count mechanism.

   o  18.  Discuss the handling of multiple valid discovery responses.

      RESOLVED: Stated that the choice must be available to the ASA but
      GRASP implementation should pick a default.

   o  19.  Should we use a text-oriented format such as JSON/CBOR
      instead of native binary TLV format?

      RESOLVED: Yes, changed to CBOR.





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   o  20.  Is the Divert option needed?  If a discovery response
      provides a valid IP address or FQDN, the recipient doesn't gain
      any extra knowledge from the Divert.  On the other hand, the
      presence of Divert informs the receiver that the target is off-
      link, which might be useful sometimes.

      RESOLVED: Decided to keep Divert option.

   o  21.  Rename the protocol as GRASP (GeneRic Autonomic Signaling
      Protocol)?

      RESOLVED: Yes, name changed.

   o  22.  Does discovery mechanism scale robustly as needed?  Need hop
      limit on relaying?

      RESOLVED: Added hop limit.

   o  23.  Need more details on TTL for caching discovery responses.

      RESOLVED: Done.

   o  24.  Do we need "fast withdrawal" of discovery responses?

      RESOLVED: This doesn't seem necessary.  If an ASA exits or stops
      supporting a given objective, peers will fail to start future
      sessions and will simply repeat discovery.

   o  25.  Does GDNP discovery meet the needs of multi-hop DNS-SD?

      RESOLVED: Decided not to consider this further as a GRASP protocol
      issue.  GRASP objectives could embed DNS-SD formats if needed.

   o  26.  Add a URL type to the locator options (for security bootstrap
      etc.)

      RESOLVED: Done, later renamed as URI.

   o  27.  Security of Flood multicasts (Section 3.5.6.1).

      RESOLVED: added text.

   o  28.  Does ACP support secure link-local multicast?

      RESOLVED by new text in the Security Considerations.

   o  29.  PEN is used to distinguish vendor options.  Would it be
      better to use a domain name?  Anything unique will do.



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      RESOLVED: Simplified this by removing PEN field and changing
      naming rules for objectives.

   o  30.  Does response to discovery require randomized delays to
      mitigate amplification attacks?

      RESOLVED: WG feedback is that it's unnecessary.

   o  31.  We have specified repeats for failed discovery etc.  Is that
      sufficient to deal with sleeping nodes?

      RESOLVED: WG feedback is that it's unnecessary to say more.

   o  32.  We have one-to-one synchronization and flooding
      synchronization.  Do we also need selective flooding to a subset
      of nodes?

      RESOLVED: This will be discussed as a protocol extension in a
      separate draft (draft-liu-anima-grasp-distribution).

   o  33.  Clarify if/when discovery needs to be repeated.

      RESOLVED: Done.

   o  34.  Clarify what is mandatory for running in ACP, expand
      discussion of security boundary when running with no ACP - might
      rely on the local PKI infrastructure.

      RESOLVED: Done.

   o  35.  State that role-based authorization of ASAs is out of scope
      for GRASP.  GRASP doesn't recognize/handle any "roles".

      RESOLVED: Done.

   o  36.  Reconsider CBOR definition for PEN syntax.  ( objective-name
      = text / [pen, text] ; pen = uint )

      RESOLVED: See issue 29.

   o  37.  Are URI locators really needed?

      RESOLVED: Yes, e.g. for security bootstrap discovery, but added
      note that addresses are the normal case (same for FQDN locators).

   o  38.  Is Session ID sufficient to identify relayed responses?
      Isn't the originator's address needed too?




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      RESOLVED: Yes, this is needed for multicast messages and their
      responses.

   o  39.  Clarify that a node will contain one GRASP instance
      supporting multiple ASAs.

      RESOLVED: Done.

   o  40.  Add a "reason" code to the DECLINE option?

      RESOLVED: Done.

   o  41.  What happens if an ASA cannot conveniently use one of the
      GRASP mechanisms?  Do we (a) add a message type to GRASP, or (b)
      simply pass the discovery results to the ASA so that it can open
      its own socket?

      RESOLVED: Both would be possible, but (b) is preferred.

   o  42.  Do we need a feature whereby an ASA can bypass the ACP and
      use the data plane for efficiency/throughput?  This would require
      discovery to return non-ACP addresses and would evade ACP
      security.

      RESOLVED: This is considered out of scope for GRASP, but a comment
      has been added in security considerations.

   o  43.  Rapid mode synchronization and negotiation is currently
      limited to a single objective for simplicity of design and
      implementation.  A future consideration is to allow multiple
      objectives in rapid mode for greater efficiency.

      RESOLVED: This is considered out of scope for this version.

   o  44.  In requirement T9, the words that encryption "may not be
      required in all deployments" were removed.  Is that OK?.

      RESOLVED: No objections.

   o  45.  Device Identity Option is unused.  Can we remove it
      completely?.

      RESOLVED: No objections.  Done.

   o  46.  The 'initiator' field in DISCOVER, RESPONSE and FLOOD
      messages is intended to assist in loop prevention.  However, we
      also have the loop count for that.  Also, if we create a new
      Session ID each time a DISCOVER or FLOOD is relayed, that ID can



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      be disambiguated by recipients.  It would be simpler to remove the
      initiator from the messages, making parsing more uniform.  Is that
      OK?

      RESOLVED: Yes. Done.

   o  47.  REQUEST is a dual purpose message (request negotiation or
      request synchronization).  Would it be better to split this into
      two different messages (and adjust various message names
      accordingly)?

      RESOLVED: Yes. Done.

   o  48.  Should the Appendix "Capability Analysis of Current
      Protocols" be deleted before RFC publication?

      RESOLVED: No (per WG meeting at IETF 96).

   o  49.  Section 3.5.1 Should say more about signaling between two
      autonomic networks/domains.

      RESOLVED: Description of separate GRASP instance added.

   o  50.  Is Rapid mode limited to on-link only?  What happens if first
      discovery responder does not support Rapid Mode?  Section 3.5.5,
      Section 3.5.6)

      RESOLVED: Not limited to on-link.  First responder wins.

   o  51.  Should flooded objectives have a time-to-live before they are
      deleted from the flood cache?  And should they be tagged in the
      cache with their source locator?

      RESOLVED: TTL added to Flood (and Discovery Response) messages.
      Cached flooded objectives must be tagged with their originating
      ASA locator, and multiple copies must be kept if necessary.

   o  52.  Describe in detail what is allowed and disallowed in an
      insecure instance of GRASP.

      RESOLVED: Done.

   o  53.  Tune IANA Considerations to support early assignment request.


   o  54.  Is there a highly unlikely race condition if two peers
      simultaneously choose the same Session ID and send each other
      simultaneous M_REQ_NEG messages?



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      RESOLVED: Yes. Enhanced text on Session ID generation, and added
      precaution when receiving a Request message.

   o  55.  Could discovery be performed over TCP?

      RESOLVED: Unicast discovery added as an option.

   o  56.  Change Session-ID to 32 bits?

      RESOLVED: Done.

   o  57.  Add M_INVALID message?

      RESOLVED: Done.

   o  58.  Maximum message size?

      RESOLVED by specifying default maximum message size (2048 bytes).

   o  59.  Add F_NEG_DRY flag to specify a "dry run" objective?.

      RESOLVED: Done.

   o  60.  Change M_FLOOD syntax to associate a locator with each
      objective?

      RESOLVED: Done.

   o  61.  Is the SONN constrained instance really needed?

      RESOLVED: Retained but only as an option.

   o  62.  Is it helpful to tag descriptive text with message names
      (M_DISCOVER etc.)?

      RESOLVED: Yes, done in various parts of the text.

Appendix C.  Change log [RFC Editor: Please remove]

   draft-ietf-anima-grasp-09, 2016-12-15:

   Protocol change: Add F_NEG_DRY flag to specify a "dry run" objective.

   Protocol change: Change M_FLOOD syntax to associate a locator with
   each objective.

   Concentrated mentions of TLS in one section, with all details out of
   scope.



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   Clarified text around constrained instances of GRASP.

   Strengthened text restricting LL addresses in locator options.

   Clarified description of rapid mode processsing.

   Specified that cached discovery results should not be returned on the
   same interface where they were learned.

   Shortened text in "High Level Design Choices"

   Dropped the word 'kernel' to avoid confusion with o/s kernel mode.

   Editorial improvements and clarifications.

   draft-ietf-anima-grasp-08, 2016-10-30:

   Protocol change: Added M_INVALID message.

   Protocol change: Increased Session ID space to 32 bits.

   Enhanced rules to avoid Session ID clashes.

   Corrected and completed description of timeouts for Request messages.

   Improved wording about exponential backoff and DoS.

   Clarified that discovery relaying is not done by limited security
   instances.

   Corrected and expanded explanation of port used for Discovery
   Response.

   Noted that Discovery message could be sent unicast in special cases.

   Added paragraph on extensibility.

   Specified default maximum message size.

   Added Appendix for sample messages.

   Added short protocol overview.

   Editorial fixes, including minor re-ordering for readability.

   draft-ietf-anima-grasp-07, 2016-09-13:

   Protocol change: Added TTL field to Flood message (issue 51).



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   Protocol change: Added Locator option to Flood message (issue 51).

   Protocol change: Added TTL field to Discovery Response message
   (corrollary to issue 51).

   Clarified details of rapid mode (issues 43 and 50).

   Description of inter-domain GRASP instance added (issue 49).

   Description of limited security GRASP instances added (issue 52).

   Strengthened advice to use TCP rather than UDP.

   Updated IANA considerations and text about well-known port usage
   (issue 53).

   Amended text about ASA authorization and roles to allow for
   overlapping ASAs.

   Added text recommending that Flood should be repeated periodically.

   Editorial fixes.

   draft-ietf-anima-grasp-06, 2016-06-27:

   Added text on discovery cache timeouts.

   Noted that ASAs that are only initiators do not need to respond to
   discovery message.

   Added text on unexpected address changes.

   Added text on robust implementation.

   Clarifications and editorial fixes for numerous review comments

   Added open issues for some review comments.

   draft-ietf-anima-grasp-05, 2016-05-13:

   Noted in requirement T1 that it should be possible to implement ASAs
   independently as user space programs.

   Protocol change: Added protocol number and port to discovery
   response.  Updated protocol description, CDDL and IANA considerations
   accordingly.





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   Clarified that discovery and flood multicasts are handled by the
   GRASP core, not directly by ASAs.

   Clarified that a node may discover an objective without supporting it
   for synchronization or negotiation.

   Added Implementation Status section.

   Added reference to SCSP.

   Editorial fixes.

   draft-ietf-anima-grasp-04, 2016-03-11:

   Protocol change: Restored initiator field in certain messages and
   adjusted relaying rules to provide complete loop detection.

   Updated IANA Considerations.

   draft-ietf-anima-grasp-03, 2016-02-24:

   Protocol change: Removed initiator field from certain messages and
   adjusted relaying requirement to simplify loop detection.  Also
   clarified narrative explanation of discovery relaying.

   Protocol change: Split Request message into two (Request Negotiation
   and Request Synchronization) and updated other message names for
   clarity.

   Protocol change: Dropped unused Device ID option.

   Further clarified text on transport layer usage.

   New text about multicast insecurity in Security Considerations.

   Various other clarifications and editorial fixes, including moving
   some material to Appendix.

   draft-ietf-anima-grasp-02, 2016-01-13:

   Resolved numerous issues according to WG discussions.

   Renumbered requirements, added D9.

   Protocol change: only allow one objective in rapid mode.

   Protocol change: added optional error string to DECLINE option.




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   Protocol change: removed statement that seemed to say that a Request
   not preceded by a Discovery should cause a Discovery response.  That
   made no sense, because there is no way the initiator would know where
   to send the Request.

   Protocol change: Removed PEN option from vendor objectives, changed
   naming rule accordingly.

   Protocol change: Added FLOOD message to simplify coding.

   Protocol change: Added SYNCH message to simplify coding.

   Protocol change: Added initiator id to DISCOVER, RESPONSE and FLOOD
   messages.  But also allowed the relay process for DISCOVER and FLOOD
   to regenerate a Session ID.

   Protocol change: Require that discovered addresses must be global
   (except during bootstrap).

   Protocol change: Receiver of REQUEST message must close socket if no
   ASA is listening for the objective.

   Protocol change: Simplified Waiting message.

   Protocol change: Added No Operation message.

   Renamed URL locator type as URI locator type.

   Updated CDDL definition.

   Various other clarifications and editorial fixes.

   draft-ietf-anima-grasp-01, 2015-10-09:

   Updated requirements after list discussion.

   Changed from TLV to CBOR format - many detailed changes, added co-
   author.

   Tightened up loop count and timeouts for various cases.

   Noted that GRASP does not provide transactional integrity.

   Various other clarifications and editorial fixes.

   draft-ietf-anima-grasp-00, 2015-08-14:

   File name and protocol name changed following WG adoption.



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   Added URL locator type.

   draft-carpenter-anima-gdn-protocol-04, 2015-06-21:

   Tuned wording around hierarchical structure.

   Changed "device" to "ASA" in many places.

   Reformulated requirements to be clear that the ASA is the main
   customer for signaling.

   Added requirement for flooding unsolicited synch, and added it to
   protocol spec.  Recognized DNCP as alternative for flooding synch
   data.

   Requirements clarified, expanded and rearranged following design team
   discussion.

   Clarified that GDNP discovery must not be a prerequisite for GDNP
   negotiation or synchronization (resolved issue 13).

   Specified flag bits for objective options (resolved issue 15).

   Clarified usage of ACP vs TLS/DTLS and TCP vs UDP (resolved issues
   9,10,11).

   Updated DNCP description from latest DNCP draft.

   Editorial improvements.

   draft-carpenter-anima-gdn-protocol-03, 2015-04-20:

   Removed intrinsic security, required external security

   Format changes to allow DNCP co-existence

   Recognized DNS-SD as alternative discovery method.

   Editorial improvements

   draft-carpenter-anima-gdn-protocol-02, 2015-02-19:

   Tuned requirements to clarify scope,

   Clarified relationship between types of objective,

   Clarified that objectives may be simple values or complex data
   structures,



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   Improved description of objective options,

   Added loop-avoidance mechanisms (loop count and default timeout,
   limitations on discovery relaying and on unsolicited responses),

   Allow multiple discovery objectives in one response,

   Provided for missing or multiple discovery responses,

   Indicated how modes such as "dry run" should be supported,

   Minor editorial and technical corrections and clarifications,

   Reorganized future work list.

   draft-carpenter-anima-gdn-protocol-01, restructured the logical flow
   of the document, updated to describe synchronization completely, add
   unsolicited responses, numerous corrections and clarifications,
   expanded future work list, 2015-01-06.

   draft-carpenter-anima-gdn-protocol-00, combination of draft-jiang-
   config-negotiation-ps-03 and draft-jiang-config-negotiation-protocol-
   02, 2014-10-08.

Appendix D.  Example Message Formats

   For readers unfamiliar with CBOR, this appendix shows a number of
   example GRASP messages conforming to the CDDL syntax given in
   Section 6.  Each message is shown three times in the following
   formats:

   1.  CBOR diagnostic notation.

   2.  Similar, but showing the names of the constants.  (Details of the
       flag bit encoding are omitted.)

   3.  Hexadecimal version of the CBOR wire format.

   Long lines are split for display purposes only.

D.1.  Discovery Example

   The initiator (2001:db8:f000:baaa:28cc:dc4c:9703:6781) multicasts a
   discovery message looking for objective EX1:







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   [1, 13948744, h'20010db8f000baaa28ccdc4c97036781', ["EX1", 5, 2, 0]]
   [M_DISCOVERY, 13948744, h'20010db8f000baaa28ccdc4c97036781',
                 ["EX1", F_SYNCH_bits, 2, 0]]
   h'84011a00d4d7485020010db8f000baaa28ccdc4c970367818463455831050200'

   A peer (2001:0db8:f000:baaa:f000:baaa:f000:baaa) responds with a
   locator:

   [2, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
                 [103, h'20010db8f000baaaf000baaaf000baaa', 6, 49443]]
   [M_RESPONSE, 13948744, h'20010db8f000baaa28ccdc4c97036781', 60000,
                 [O_IPv6_LOCATOR, h'20010db8f000baaaf000baaaf000baaa',
                  IPPROTO_TCP, 49443]]
   h'85021a00d4d7485020010db8f000baaa28ccdc4c9703678119ea6084186750
     20010db8f000baaaf000baaaf000baaa0619c123'

D.2.  Flood Example

   The initiator multicasts a flood message.  The single objective has a
   null locator.  There is no response:

[9, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,
             [["EX1", 5, 2, ["Example 1 value=", 100]],[] ] ]
[M_FLOOD, 3504974, h'20010db8f000baaa28ccdc4c97036781', 10000,
             [["EX1", F_SYNCH_bits, 2, ["Example 1 value=", 100]],[] ] ]
h'86091a00357b4e5020010db8f000baaa28ccdc4c97036781192710
  828463455831050282704578616d706c6520312076616c75653d186480'

D.3.  Synchronization Example

   Following successful discovery of objective EX2, the initiator
   unicasts a request:

   [4, 4038926, ["EX2", 5, 5, 0]]
   [M_REQ_SYN, 4038926, ["EX2", F_SYNCH_bits, 5, 0]]
   h'83041a003da10e8463455832050500'

   The peer responds with a value:

 [8, 4038926, ["EX2", 5, 5, ["Example 2 value=", 200]]]
 [M_SYNCH, 4038926, ["EX2", F_SYNCH_bits, 5, ["Example 2 value=", 200]]]
 h'83081a003da10e8463455832050582704578616d706c6520322076616c75653d18c8'

D.4.  Simple Negotiation Example

   Following successful discovery of objective EX3, the initiator
   unicasts a request:




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   [3, 802813, ["EX3", 3, 6, ["NZD", 47]]]
   [M_REQ_NEG, 802813, ["EX3", F_NEG_bits, 6, ["NZD", 47]]]
   h'83031a000c3ffd8463455833030682634e5a44182f'

   The peer responds with immediate acceptance.  Note that no objective
   is needed, because the initiator's request was accepted without
   change:

   [6, 802813, [101]]
   [M_END , 802813, [O_ACCEPT]]
   h'83061a000c3ffd811865'

D.5.  Complete Negotiation Example

   Again the initiator unicasts a request:

   [3, 13767778, ["EX3", 3, 6, ["NZD", 410]]]
   [M_REQ_NEG, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 410]]]
   h'83031a00d214628463455833030682634e5a4419019a'

   The responder starts to negotiate (making an offer):

   [5, 13767778, ["EX3", 3, 6, ["NZD", 80]]]
   [M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 6, ["NZD", 80]]]
   h'83051a00d214628463455833030682634e5a441850'

   The initiator continues to negotiate (reducing its request, and note
   that the loop count is decremented):

   [5, 13767778, ["EX3", 3, 5, ["NZD", 307]]]
   [M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 5, ["NZD", 307]]]
   h'83051a00d214628463455833030582634e5a44190133'

   The responder asks for more time:

   [7, 13767778, 34965]
   [M_WAIT, 13767778, 34965]
   h'83071a00d21462198895'

   The responder continues to negotiate (increasing its offer):

   [5, 13767778, ["EX3", 3, 4, ["NZD", 120]]]
   [M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 4, ["NZD", 120]]]
   h'83051a00d214628463455833030482634e5a441878'

   The initiator continues to negotiate (reducing its request):





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   [5, 13767778, ["EX3", 3, 3, ["NZD", 246]]]
   [M_NEGOTIATE, 13767778, ["EX3", F_NEG_bits, 3, ["NZD", 246]]]
   h'83051a00d214628463455833030382634e5a4418f6'

   The responder refuses to negotiate further:

   [6, 13767778, [102, "Insufficient funds"]]
   [M_END , 13767778, [O_DECLINE, "Insufficient funds"]]
   h'83061a00d2146282186672496e73756666696369656e742066756e6473'

   This negotiation has failed.  If either side had sent [M_END,
   13767778, [O_ACCEPT]] it would have succeeded, converging on the
   objective value in the preceding M_NEGOTIATE.  Note that apart from
   the initial M_REQ_NEG, the process is symmetrical.

Appendix E.  Capability Analysis of Current Protocols

   This appendix discusses various existing protocols with properties
   related to the requirements described in Section 2.  The purpose is
   to evaluate whether any existing protocol, or a simple combination of
   existing protocols, can meet those requirements.

   Numerous protocols include some form of discovery, but these all
   appear to be very specific in their applicability.  Service Location
   Protocol (SLP) [RFC2608] provides service discovery for managed
   networks, but requires configuration of its own servers.  DNS-SD
   [RFC6763] combined with mDNS [RFC6762] provides service discovery for
   small networks with a single link layer.  [RFC7558] aims to extend
   this to larger autonomous networks but this is not yet standardized.
   However, both SLP and DNS-SD appear to target primarily application
   layer services, not the layer 2 and 3 objectives relevant to basic
   network configuration.  Both SLP and DNS-SD are text-based protocols.

   Routing protocols are mainly one-way information announcements.  The
   receiver makes independent decisions based on the received
   information and there is no direct feedback information to the
   announcing peer.  This remains true even though the protocol is used
   in both directions between peer routers; there is state
   synchronization, but no negotiation, and each peer runs its route
   calculations independently.

   Simple Network Management Protocol (SNMP) [RFC3416] uses a command/
   response model not well suited for peer negotiation.  Network
   Configuration Protocol (NETCONF) [RFC6241] uses an RPC model that
   does allow positive or negative responses from the target system, but
   this is still not adequate for negotiation.





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   There are various existing protocols that have elementary negotiation
   abilities, such as Dynamic Host Configuration Protocol for IPv6
   (DHCPv6) [RFC3315], Neighbor Discovery (ND) [RFC4861], Port Control
   Protocol (PCP) [RFC6887], Remote Authentication Dial In User Service
   (RADIUS) [RFC2865], Diameter [RFC6733], etc.  Most of them are
   configuration or management protocols.  However, they either provide
   only a simple request/response model in a master/slave context or
   very limited negotiation abilities.

   There are some signaling protocols with an element of negotiation.
   For example Resource ReSerVation Protocol (RSVP) [RFC2205] was
   designed for negotiating quality of service parameters along the path
   of a unicast or multicast flow.  RSVP is a very specialised protocol
   aimed at end-to-end flows.  However, it has some flexibility, having
   been extended for MPLS label distribution [RFC3209].  A more generic
   design is General Internet Signalling Transport (GIST) [RFC5971], but
   it is complex, tries to solve many problems, and is also aimed at
   per-flow signaling across many hops rather than at device-to-device
   signaling.  However, we cannot completely exclude extended RSVP or
   GIST as a synchronization and negotiation protocol.  They do not
   appear to be directly useable for peer discovery.

   We now consider two protocols that are works in progress at the time
   of this writing.  Firstly, RESTCONF [I-D.ietf-netconf-restconf] is a
   protocol intended to convey NETCONF information expressed in the YANG
   language via HTTP, including the ability to transit HTML
   intermediaries.  While this is a powerful approach in the context of
   centralised configuration of a complex network, it is not well
   adapted to efficient interactive negotiation between peer devices,
   especially simple ones that might not include YANG processing
   already.

   Secondly, we consider Distributed Node Consensus Protocol (DNCP)
   [RFC7787].  This is defined as a generic form of state
   synchronization protocol, with a proposed usage profile being the
   Home Networking Control Protocol (HNCP) [RFC7788] for configuring
   Homenet routers.  A specific application of DNCP for autonomic
   networking was proposed in [I-D.stenberg-anima-adncp].

   DNCP "is designed to provide a way for each participating node to
   publish a set of TLV (Type-Length-Value) tuples, and to provide a
   shared and common view about the data published... DNCP is most
   suitable for data that changes only infrequently... If constant rapid
   state changes are needed, the preferable choice is to use an
   additional point-to-point channel..."

   Specific features of DNCP include:




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   o  Every participating node has a unique node identifier.

   o  DNCP messages are encoded as a sequence of TLV objects, sent over
      unicast UDP or TCP, with or without (D)TLS security.

   o  Multicast is used only for discovery of DNCP neighbors when lower
      security is acceptable.

   o  Synchronization of state is maintained by a flooding process using
      the Trickle algorithm.  There is no bilateral synchronization or
      negotiation capability.

   o  The HNCP profile of DNCP is designed to operate between directly
      connected neighbors on a shared link using UDP and link-local IPv6
      addresses.

   DNCP does not meet the needs of a general negotiation protocol,
   because it is designed specifically for flooding synchronization.
   Also, in its HNCP profile it is limited to link-local messages and to
   IPv6.  However, at the minimum it is a very interesting test case for
   this style of interaction between devices without needing a central
   authority, and it is a proven method of network-wide state
   synchronization by flooding.

   The Server Cache Synchronization Protocol (SCSP) [RFC2334] also
   describes a method for cache synchronization and cache replication
   among a group of nodes.

   A proposal was made some years ago for an IP based Generic Control
   Protocol (IGCP) [I-D.chaparadza-intarea-igcp].  This was aimed at
   information exchange and negotiation but not directly at peer
   discovery.  However, it has many points in common with the present
   work.

   None of the above solutions appears to completely meet the needs of
   generic discovery, state synchronization and negotiation in a single
   solution.  Many of the protocols assume that they are working in a
   traditional top-down or north-south scenario, rather than a fluid
   peer-to-peer scenario.  Most of them are specialized in one way or
   another.  As a result, we have not identified a combination of
   existing protocols that meets the requirements in Section 2.  Also,
   we have not identified a path by which one of the existing protocols
   could be extended to meet the requirements.








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Authors' Addresses

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany

   Email: cabo@tzi.org


   Brian Carpenter (editor)
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com


   Bing Liu (editor)
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus
   No.156 Beiqing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: leo.liubing@huawei.com






















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