Validate Bidirectional Forwarding Detection (BFD) integration with customer eBGP peering on the DUT across 802.1Q subinterfaces. Verify sub-second failure detection, timer negotiation, dampening behavior, and immediate BGP session teardown upon BFD link state transitions.

• TESTBED_DUT_ATE_2LINKS (ATE Port 1 simulating Customer CE router with BFD enabled).

graph LR;
  ce1[ATE Port 1: Customer CE] -- "802.1Q VLAN 100 (eBGP + BFD)" --> dut1[DUT Port 1.100: Tenant VRF ce1]

1. Configure tenant VRF ce1 and subinterface Port1.100 (VLAN 100, IP 192.0.2.1/30).
2. Configure eBGP neighbor 192.0.2.2 (AS 65001) in VRF ce1.
3. Enable BFD under the BGP neighbor container (enable-bfd) and configure BFD interface parameters:
   • desired-minimum-tx-interval: 300000 (300 ms)
   • required-minimum-receive: 300000 (300 ms)
   • detection-multiplier: 3
4. Configure ATE CE1 with matching BFD configuration.

• Step 1: Start BFD and BGP on ATE CE1.
• Step 2: Verify BFD session state transitions to UP via OpenConfig telemetry /bfd/interfaces/interface/peers/peer/state/session-state.
• Step 3: Verify negotiated timers match: transmitted interval $\le 300$ ms, received interval $\le 300$ ms (/bfd/interfaces/interface/peers/peer/state/remote-minimum-receive-interval).
• Step 4: Verify BGP session transitions to ESTABLISHED.

• Step 1: Inject steady traffic stream from ATE CE1 through DUT.
• Step 2: Abruptly stop BFD control packets from ATE CE1 (simulating unidirectional link failure or remote peer crash) without sending BGP FIN/RST or BGP Notification.
• Step 3: Verify DUT detects BFD failure within detection timeout ($3 \times 300\text{ ms} = 900\text{ ms}$) and reports diagnostic code at /bfd/interfaces/interface/peers/peer/state/local-diagnostic-code.
• Step 4: Verify DUT immediately terminates the BGP session and withdraws customer routes without waiting for standard BGP hold timer expiry (e.g. 90 seconds).
• Step 5: Verify telemetry state updates within 1 second.

• Step 1: Flap BFD session 3 consecutive times in 10 seconds.
• Step 2: Verify BFD dampening or hold-down timer triggers to prevent control-plane starvation.
• Step 3: Verify BGP session stays down during the dampening window and stabilizes once flaps subside.

{
  "network-instances": {
    "network-instance": [
      {
        "name": "ce1",
        "protocols": {
          "protocol": [
            {
              "identifier": "openconfig-policy-types:BGP",
              "name": "BGP",
              "bgp": {
                "neighbors": {
                  "neighbor": [
                    {
                      "neighbor-address": "192.0.2.2",
                      "config": {
                        "neighbor-address": "192.0.2.2",
                        "peer-as": 65001
                      },
                      "enable-bfd": {
                        "config": {
                          "enabled": true
                        }
                      }
                    }
                  ]
                }
              }
            }
          ]
        }
      }
    ]
  }
}

paths:
  # BFD Configuration and Operational State
  /bfd/interfaces/interface/config/desired-minimum-tx-interval:
  /bfd/interfaces/interface/config/required-minimum-receive:
  /bfd/interfaces/interface/config/detection-multiplier:
  /bfd/interfaces/interface/peers/peer/state/session-state:
  /bfd/interfaces/interface/peers/peer/state/local-diagnostic-code:
  /bfd/interfaces/interface/peers/peer/state/remote-minimum-receive-interval:
  # BGP Dependency State
  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/enable-bfd/config/enabled:
  /network-instances/network-instance/protocols/protocol/bgp/neighbors/neighbor/state/session-state:

rpcs:
  gnmi:
    gNMI.Get:
    gNMI.Subscribe:

• FFF