🧪 Lab 03 · Sub-Second WAN Link Failover with BFD¶

✅ Validated on Arista cEOS 4.32.0F BFD engine.

Time: ~45 minutes · Tools: BFD (Bidirectional Forwarding Detection)

Quick Start — Step-by-Step Execution Guide (Location: labs/wan-edge-lab/)

Step 1 · Deploy the Lab Fabric (if not already running)

cd labs/wan-edge-lab
sudo containerlab deploy -t topology.clab.yml --max-workers 1

Step 2 · Launch the Fully Guided Interactive Walkthrough

./run.sh --guided

Alternative Execution Options (Automated Push or Manual CLI)

Fast Automated Script Push:

./run.sh 01          # apply + verify step 01 automatically
./run.sh --all       # run all steps in order

Manual Line-by-Line CLI Execution: Interactive CLI shell on any container node:
```
docker exec -it clab-wan-edge-lab-wan-edge1 Cli
```

🧠 Technology Deep Dive: BFD vs. Standard BGP Timers¶

Standard BGP uses a 60-second Keepalive and a 180-second Hold-Timer. If an intermediate fiber transport fails without an interface link down signal, BGP can take 3 minutes to detect the failure!

BFD (Bidirectional Forwarding Detection) sends micro-hello control packets at sub-second intervals (e.g., 300ms intervals with a multiplier of 3 → 900ms failure detection):

interface Ethernet1
   bfd interval 300 min_rx 300 multiplier 3
!
router bgp 65000
   neighbor 198.51.100.2 fall-over bfd

✅ DONE when show bfd neighbors displays active BFD session in Up state with 300ms timers.