Why UE cannot receive ICMP response from gNB (UERANSIM + Free5GC)

[Shanola]

Hello @aligungr and community,

I'm using UERANSIM v3.2.3 and Free5GC v3.0.6.

Currently I'm building an environment based on Environment setup of multiple SMF, DNN, and UPF (including ULCL) of Free5GC, but to divided one UERANSIM VM into 2 VMs (one is UE and the other one is gNB)

• Original topology (screeshot from Free5GC's video):
  

• New topology (divide UERANSIM VM into 2 VMs):
  

I've successfully test original topology with Ping command, but when I divided UERANSIM VM into 2 VMs, there're two results:

1. UE1 ping to 8.8.8.8 (DNN: Internet): Failed
2. UE2 ping to 8.8.8.8 (DNN: IMS): Success

I found that the ICMP request can go to the internet, but the ICMP reply stops at gNB, which means gNB receives ICMP reply from I-UPF, but it doesn't forward the packet anymore!

So I wonder if I miss some configuration or misuse the UERANSIM software?

Here are my YAML files:

• free5gc-ue1.yaml

  # IMSI number of the UE. IMSI = [MCC|MNC|MSISDN] (In total 15 digits)
  supi: 'imsi-208930000000003'
  # Mobile Country Code value of HPLMN
  mcc: '208'
  # Mobile Network Code value of HPLMN (2 or 3 digits)
  mnc: '93'
  
  # Permanent subscription key
  key: '8baf473f2f8fd09487cccbd7097c6862'
  # Operator code (OP or OPC) of the UE
  op: '8e27b6af0e692e750f32667a3b14605d'
  # This value specifies the OP type and it can be either 'OP' or 'OPC'
  opType: 'OPC'
  # Authentication Management Field (AMF) value
  amf: '8000'
  # IMEI number of the device. It is used if no SUPI is provided
  imei: '356938035643803'
  # IMEISV number of the device. It is used if no SUPI and IMEI is provided
  imeiSv: '4370816125816151'
  
  # List of gNB IP addresses for Radio Link Simulation
  gnbSearchList:
    - 192.168.0.131
  
  # UAC Access Identities Configuration
  uacAic:
    mps: false
    mcs: false
  
  # UAC Access Control Class
  uacAcc:
    normalClass: 0
    class11: false
    class12: false
    class13: false
    class14: false
    class15: false
  
  # Initial PDU sessions to be established
  sessions:
    - type: 'IPv4'
      apn: 'internet'
      slice:
        sst: 0x01
        sd: 0x010203
  
  # Configured NSSAI for this UE by HPLMN
  configured-nssai:
    - sst: 0x01
      sd: 0x010203
  
  # Default Configured NSSAI for this UE
  default-nssai:
    - sst: 1
      sd: 1
  
  # Supported encryption algorithms by this UE
  integrity:
    IA1: true
    IA2: true
    IA3: true
  
  # Supported integrity algorithms by this UE
  ciphering:
    EA1: true
    EA2: true
    EA3: true
  
  # Integrity protection maximum data rate for user plane
  integrityMaxRate:
    uplink: 'full'
    downlink: 'full'
  

• free5gc-ue2.yaml

  # IMSI number of the UE. IMSI = [MCC|MNC|MSISDN] (In total 15 digits)
  supi: 'imsi-208930000000004'
  # Mobile Country Code value of HPLMN
  mcc: '208'
  # Mobile Network Code value of HPLMN (2 or 3 digits)
  mnc: '93'
  
  # Permanent subscription key
  key: '8baf473f2f8fd09487cccbd7097c6862'
  # Operator code (OP or OPC) of the UE
  op: '8e27b6af0e692e750f32667a3b14605d'
  # This value specifies the OP type and it can be either 'OP' or 'OPC'
  opType: 'OPC'
  # Authentication Management Field (AMF) value
  amf: '8000'
  # IMEI number of the device. It is used if no SUPI is provided
  imei: '356938035643803'
  # IMEISV number of the device. It is used if no SUPI and IMEI is provided
  imeiSv: '4370816125816151'
  
  # List of gNB IP addresses for Radio Link Simulation
  gnbSearchList:
    - 192.168.0.131
  
  # UAC Access Identities Configuration
  uacAic:
    mps: false
    mcs: false
  
  # UAC Access Control Class
  uacAcc:
    normalClass: 0
    class11: false
    class12: false
    class13: false
    class14: false
    class15: false
  
  # Initial PDU sessions to be established
  sessions:
    - type: 'IPv4'
      apn: 'IMS'
      slice:
        sst: 0x01
        sd: 0x112233
  
  # Configured NSSAI for this UE by HPLMN
  configured-nssai:
    - sst: 0x01
      sd: 0x112233
  
  # Default Configured NSSAI for this UE
  default-nssai:
    - sst: 1
      sd: 1
  
  # Supported encryption algorithms by this UE
  integrity:
    IA1: true
    IA2: true
    IA3: true
  
  # Supported integrity algorithms by this UE
  ciphering:
    EA1: true
    EA2: true
    EA3: true
  
  # Integrity protection maximum data rate for user plane
  integrityMaxRate:
    uplink: 'full'
    downlink: 'full'
  

• free5gc-gnb.yaml

  mcc: '208'          # Mobile Country Code value
  mnc: '93'           # Mobile Network Code value (2 or 3 digits)
  
  nci: '0x000000010'  # NR Cell Identity (36-bit)
  idLength: 32        # NR gNB ID length in bits [22...32]
  tac: 1              # Tracking Area Code
  
  linkIp: 192.168.0.131   # gNB's local IP address for Radio Link Simulation (Usually same with local IP)
  ngapIp: 172.16.2.1   # gNB's local IP address for N2 Interface (Usually same with local IP)
  gtpIp: 172.16.3.1    # gNB's local IP address for N3 Interface (Usually same with local IP)
  
  # List of AMF address information
  amfConfigs:
    - address: 172.16.2.100
      port: 38412
  
  # List of supported S-NSSAIs by this gNB
  slices:
    - sst: 0x1
      sd: 0x010203
    - sst: 0x1
      sd: 0x112233
  
  # Indicates whether or not SCTP stream number errors should be ignored.
  ignoreStreamIds: true
  

There's my setting note which's more detail, thank you!
multiple SMF, UPF with seperate UE and gNB

[Shanola]

The reason why UE cannot receive reply have something to do with ARP.
After setting all interface in the same LAN, the problem is fix.