Inbound Steering: AS-Path Prepending (Primary/Backup eBGP)

Bundle lab

Advanced CCNP BGP lab: Build parallel eBGP sessions between two ASes over primary and backup /30 links. Originate a service prefix from AS 65001 and influence AS 65002's inbound path by applying outbound AS-path prepending on the backup session only. Validate best-path selection and next-hop on the neighbor, and confirm reachability from hosts.

Learning objectives

• Stand up two parallel eBGP sessions between different ASNs on separate /30s
• Originate an exact-match prefix using the network ... mask command
• Apply a route-map with set as-path prepend on a specific neighbor outbound
• Validate that the neighbor prefers the primary path via shortest AS-path
• Troubleshoot common issues: missing mask on network, remote-as mismatch, misapplied route-map direction

Troubleshooting focus

• If the neighbor does not learn the prefix, check the exact-match network ... mask and ensure the route exists in the RIB
• If only one BGP session forms, validate both sides' neighbor remote-as values and interface IPs
• If inbound preference does not shift, ensure the prepend is applied on the BACKUP session outbound and that the AS sequence includes the local AS repeated
• If host pings fail, confirm both sides advertise their LANs or use the advertised loopback target