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Chapter 30. Using LLDP to debug network configuration problems

You can use the Link Layer Discovery Protocol (LLDP) to debug network configuration problems in the topology. This means that, LLDP can report configuration inconsistencies with other hosts or routers and switches.

30.1. Debugging an incorrect VLAN configuration using LLDP information

If you configured a switch port to use a certain VLAN and a host does not receive these VLAN packets, you can use the Link Layer Discovery Protocol (LLDP) to debug the problem. Perform this procedure on the host that does not receive the packets.

Prerequisites

  • The nmstate package is installed.
  • The switch supports LLDP.
  • LLDP is enabled on neighbor devices.

Procedure

  1. Create the ~/enable-LLDP-enp1s0.yml file with the following content: 

    interfaces:
  - name: enp1s0
    type: ethernet
    lldp:
      enabled: true

  2. Use the ~/enable-LLDP-enp1s0.yml file to enable LLDP on interface enp1s0: 

    # nmstatectl apply ~/enable-LLDP-enp1s0.yml

  3. Display the LLDP information: 

    # nmstatectl show enp1s0
- name: enp1s0
  type: ethernet
  state: up
  ipv4:
    enabled: false
    dhcp: false
  ipv6:
    enabled: false
    autoconf: false
    dhcp: false
  lldp:
    enabled: true
    neighbors:
    - - type: 5
        system-name: Summit300-48
      - type: 6
        system-description: Summit300-48 - Version 7.4e.1 (Build 5)
          05/27/05 04:53:11
      - type: 7
        system-capabilities:
        - MAC Bridge component
        - Router
      - type: 1
        _description: MAC address
        chassis-id: 00:01:30:F9:AD:A0
        chassis-id-type: 4
      - type: 2
        _description: Interface name
        port-id: 1/1
        port-id-type: 5
      - type: 127
        ieee-802-1-vlans:
        - name: v2-0488-03-0505
          vid: 488
        oui: 00:80:c2
        subtype: 3
      - type: 127
        ieee-802-3-mac-phy-conf:
          autoneg: true
          operational-mau-type: 16
          pmd-autoneg-cap: 27648
        oui: 00:12:0f
        subtype: 1
      - type: 127
        ieee-802-1-ppvids:
        - 0
        oui: 00:80:c2
        subtype: 2
      - type: 8
        management-addresses:
        - address: 00:01:30:F9:AD:A0
          address-subtype: MAC
          interface-number: 1001
          interface-number-subtype: 2
      - type: 127
        ieee-802-3-max-frame-size: 1522
        oui: 00:12:0f
        subtype: 4
  mac-address: 82:75:BE:6F:8C:7A
  mtu: 1500

  4. Verify the output to ensure that the settings match your expected configuration. For example, the LLDP information of the interface connected to the switch shows that the switch port this host is connected to uses VLAN ID 448: 

    - type: 127
        ieee-802-1-vlans:
        - name: v2-0488-03-0505
          vid: 488

    If the network configuration of the enp1s0 interface uses a different VLAN ID, change it accordingly.

Additional resources

Configuring VLAN tagging