BGP Route Not Being Advertised to Peer
Presenting Symptom
A BGP route is not being advertised to a peer, even though it exists in the BGP table.
Network Context
Two Cisco routers (R1 and R2) are configured as BGP peers in a small enterprise network. R1 has a loopback interface with an IP address that it should advertise via BGP. Both routers run IOS 15.x. The BGP session is established, but the route is missing from R2's BGP table.
Diagnostic Steps
Check BGP neighbor status
show ip bgp summaryBGP router identifier 192.168.1.1, local AS number 65001 BGP table version is 3, main routing table version 3 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.168.2.2 4 65002 10 10 3 0 0 00:05:32 0
Verify that the neighbor state is 'Established' (State/PfxRcd shows number of prefixes received). If not established, troubleshoot BGP session. Here it is established but 0 prefixes received.
Check BGP table on the advertising router
show ip bgpBGP table version is 3, local router ID is 192.168.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.0.0.0/24 0.0.0.0 0 32768 iConfirm the route exists in the BGP table. The '>' indicates it is the best path. If the route is missing, check network statement or redistribution.
Check BGP neighbor advertised routes
show ip bgp neighbors 192.168.2.2 advertised-routesBGP table version is 3, local router ID is 192.168.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 10.0.0.0/24 0.0.0.0 0 32768 iIf the route appears here, it is being sent to the neighbor. If not, the route is not being advertised due to missing network statement, prefix-list, or route-map.
Check BGP configuration for network statement
show running-config | section router bgprouter bgp 65001 bgp log-neighbor-changes network 10.0.0.0 mask 255.255.255.0 neighbor 192.168.2.2 remote-as 65002
Ensure the network statement matches the route exactly. If missing, the route will not be advertised. Also check for any outbound filter (prefix-list, route-map) that might block the route.
Root Cause
The network statement for 10.0.0.0/24 is missing from the BGP configuration on R1, or the route is not present in the routing table (e.g., the loopback interface is down).
Resolution
Verification
Run 'show ip bgp neighbors 192.168.2.2 advertised-routes' to see the route now listed. Also on R2, run 'show ip bgp' to see the received route. Expected output on R2: 'BGP table version is ... *> 10.0.0.0/24 ...'.
Prevention
1. Always verify that the network statement matches the exact prefix and mask in the routing table. 2. Use 'show ip bgp neighbors <ip> advertised-routes' after configuration to confirm advertisement. 3. Implement BGP configuration checks using automation or templates to avoid missing network statements.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario may appear as a troubleshooting question where you must identify why a BGP route is not being advertised. The exam tests understanding of BGP network statements, neighbor relationships, and verification commands. Key fact: A route must be in the routing table and matched by a network statement (or redistribution) to be advertised.
Exam Tips
Remember that the network statement in BGP does not create the route; it only advertises an existing route from the routing table.
Use 'show ip bgp neighbors <ip> advertised-routes' to see what is being sent to a neighbor; this is a common exam command.
If a route is not advertised, check both the BGP table and the routing table for the route's existence.
Commands Used in This Scenario
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