BGP Lab 7: Filtering Advertised Prefixes (Prefix-List)

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Deploy eBGP between two routers and precisely control which locally-originated networks are advertised to a neighbor using an outbound prefix-list. R1 originates four /24 loopback routes but advertises only two to R2. Verify using IOS show commands and basic host reachability checks.

Learning objectives

• Configure an eBGP peering over a point-to-point /30 with correct remote-as values
• Originate exact-match routes into BGP using the network ... mask command
• Build and apply an outbound ip prefix-list to control advertised prefixes
• Verify advertised-routes and received routes with show ip bgp neighbors and show ip bgp
• Differentiate local BGP table visibility from eBGP neighbor visibility

Troubleshooting focus

• Diagnose and resolve the introduced fault: Neighbor/adjacency formation, participating interfaces, and route propagation checks.
• Verify every link's interface status and IP addressing (`show ip interface brief`) and correct any interface that is down or misaddressed.
• Confirm each device's running configuration matches the lab objective, and bring any interface, route, or service that is not in its expected state back to health.
• Trace end-to-end reachability with ping/traceroute and isolate the first hop where forwarding fails.