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🧪 Lab 02 · Inbound & Outbound BGP Traffic Engineering

✅ Validated on Arista cEOS 4.32.0F.

Time: ~45 minutes · Tools: Route Maps, AS-PATH Prepending, BGP Communities

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: Steering Traffic Across Dual ISPs

When multihomed to two ISPs, BGP path selection determines how outbound and inbound traffic flows:

1. Outbound Traffic Control (LOCAL_PREF)

LOCAL_PREF is an iBGP-only attribute passed between wan-edge1 and wan-edge2. Higher LOCAL_PREF values win: - Primary ISP A (198.51.100.2): LOCAL_PREF 200 (Preferred) - Backup ISP B (203.0.113.2): LOCAL_PREF 100

2. Inbound Traffic Control (AS-PATH Prepending)

To force external networks to prefer Primary ISP A for inbound traffic, wan-edge2 prepends its own Autonomous System number multiple times (65000 65000 65000) towards Backup ISP B:

route-map PREPEND-OUT permit 10
   set as-path prepend 65000 65000 65000

✅ DONE when show ip route bgp on external networks prefers Primary ISP A due to shorter AS-PATH length.