netbox-kea-dhcp

Enable use of NetBox as a subnet configuration source for ISC Kea DHCP server.

netbox-kea-dhcp is a one-way sync daemon that exports NetBox prefixes, IP ranges and IP addresses to respectively DHCP subnets, pools and host reservations. It listens for NetBox webhook events, and each time a change occured, it queries NetBox for the full changed data and update Kea throught its API.

The program has two modes of operation:

• Full sync at program startup: overwrite current DHCP subnets with new ones exported from NetBox.
• Continuous event-driven sync: listen for NetBox webhook events and update DHCP configuration accordingly.

Key features

• Automatic sync from Netbox to Kea DHCP with virtualy no delay.
• Update Kea configuration throught its control agent API: no direct configuration file overwrites, let’s the control agent manage the runtime and permanent configuration.
• Only use open source Kea API commands (no ISC paid subscription required).
• Submit new exported configuration to Kea check before applying it to runtime configuration.
• Query NetBox only for the objects concerned by the event (incremental sync).
• Get all NetBox data throught the well maintained pynetbox library: unique interface, loose dependency with NetBox internals (only with its API), reduced code to maintain.
• Customizable NetBox query filters.
• Customizable mapping between Netbox object attributes and DHCP settings.

Requirements

Python: >= 3.8 (tested on 3.10 but may works down to 3.8).

Netbox: validated on API version 3.4.

ISC Kea DHCP: validated on version 2.2.0.

Install

With pip

netbox-kea-dhcp is available on PyPi and can be installed with pip install netbox-kea-dhcp.

With pipx

A convenient way is to use pipx to install the application in an isolated environnement.

Install pipx (below is for Linux, see pipx homepage for other systems):

python3 -m pip install --user pipx
python3 -m pipx ensurepath

Install netbox-kea-dhcp from PyPi in a isolated environnement:

pipx install netbox-kea-dhcp

Run:

netbox-kea-dhcp --help

Quick start

Sync at startup then listen for netbox events:

netbox-kea-dhcp --netbox-url http://netbox-host \
    --netbox-token 0123456789ABCDEF \
    --kea-url http://kea-api-host --sync-now --listen -v

The default mapping between netbox and Kea is:

• prefixes are exported to subnets.

• IP ranges are exported to pools. Custom status value dhcp may have to be created in netbox configuration file (netbox-community/netbox#8054):

  FIELD_CHOICES = {
    'ipam.IPRange.status+': (
        ('dhcp', 'DHCP', 'red'),
    )
  }

• IP Addresses are exported to reservations. Hardware address is mapped with IP address custom field dhcp_reservation_hw_address if it exists and is non null, otherwise it is mapped with the MAC address of the assigned object.

At least one Netbox webhook needs to be configured for event listening. It has to notify all actions on DHCP-relevant objects:

• Content types:
  • IPAM: Prefix, IP Range, IP addresse.
  • DCIM: Interface, Device.
  • Virtualization: Interface, Virtual Machine.
• Events: Creations, Updates, Deletions.
• HTTP Request:
  • URL: http://{netbox-connector-host}:{port}/event/{free-text}/
  • HTTP Method: POST.

The field free-text is necessary to define several webhooks with same events. The connector only uses it in logs.

More help with netbox-kea-dhcp --help and in the configuration file example under examples/ (or under ~/.local/pipx/venvs/netbox-kea-dhcp/lib/python3.10/site-packages/examples/ if app was installed with pipx).

Recommended Netbox webhooks

Sysadmins should set several webhooks with conditions and restricted body template, in order to filter events and avoid unecessary network and CPU load.

Below is a recommended webhook set-up. It assumes that DHCP hardware addresses are apped with netbox interface MAC addresses. If interfaces are not used (i.e. hardware addresses are only mapped with a custom field defined in netbox IP addresses), webhooks on (vm) interfaces, (virtual) devices are not needed.

Common to all webhooks:

• HTTP Request:

  • URL: http://{netbox-connector-host}:{port}/event/{optional-free-text}/
  • HTTP Method: POST.

• Body template:

  { "event": "{{ event }}",
    "model": "{{ model }}",
    "data": { "id": {{ data["id"] }} }
  }

Webhook 1:

• Content types: IPAM > Prefix, IPAM > IP Range, IPAM > IP Address, DCIM > Device, DCIM > Interface, Virtualization > Virtual Machine, Virtualization > Interface.
• Events: Updates
• Conditions: none

Webhook 2:

• Content types: IPAM > IP Address

• Events: Creations, Deletions

• Conditions:

  { "and": [ { "attr": "status.value", "value": "dhcp" } ] }

Webhook 3:

• Content types: IPAM > IP Range

• Events: Creations, Deletions

• Conditions (note: you may have to customize status values to add dhcp):

  { "and": [ { "attr": "status.value", "value": "dhcp"} ] }

Webhook 4:

• Content types: IPAM > Prefix

• Events: Creations, Deletions

• Conditions: none, or a custom field

  { "and": [ { "attr": "custom_fields.dhcp_enabled", "value": true } ] }

It’s also recommended to set a TLS-enabled reverse proxy in front of netbox-kea-dhcp.

Limitations

• When a change occured, the whole DHCP configuration is gotten from Kea, modified, and sent back. It may put some stress on the DHCP server in case of frequent changes. This is a limitation of Kea open source commands. A better update granularity would require an ISC paid subscription.
• When Kea URI is of the form file:///path/to/kea-config, config is written to the file in an unsafe manner: if the write fails, the file will be inconsistent. This is because the file feature is intended for tests.