Each ticket gives a symptom and output from one router. The addresses are the course lab addresses.
Ticket 1: ISP A never comes up
R1#show ip bgp summary | begin Neighbor Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 192.0.2.1 4 64501 0 0 1 0 0 00:09:30 Active
Show the cause
The link works, so the TCP connection is the problem. Check that ISP A has a neighbour statement for 192.0.2.2 with remote AS 64500, and that no access list blocks port 179. Here ISP A had no neighbour entry for R1, so it never answered. Add it and the state moves to Established.
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Ticket 2: the log shows a bad peer AS
R1#show logging | include BGP %BGP-3-NOTIFICATION: sent to neighbor 192.0.2.1 2/2 (peer in wrong AS) 2 bytes FDE5
Show the cause
FDE5 is 64997 in decimal, not 64501. The neighbour statement on R1 claims the wrong remote AS, or the other side is running a different AS than agreed. Compare neighbor 192.0.2.1 remote-as with what ISP A says, and fix whichever is wrong.
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Ticket 3: R2 sees the R1 path as not valid
R2#show ip bgp Network Next Hop Metric LocPrf Weight Path i 203.0.113.0 192.0.2.1 0 100 0 64501 i *> 203.0.113.0 192.0.2.5 0 0 64502 i
Show the cause
The R1 path has no * because its next hop, 192.0.2.1, is on R1's ISP link and R2 cannot reach it. The path is not valid, so it cannot be a backup if ISP B fails. Add neighbor 10.255.0.2 next-hop-self on R1 and clear soft out.
Ticket 4: ISP A does not learn the company prefix
R1#show ip bgp neighbors 192.0.2.1 advertised-routes Total number of prefixes 0
Show the cause
A network statement advertises a route only if the exact prefix exists in the routing table. If the LAN interface is down or its mask differs, nothing matches. Check show ip route 198.51.100.0. If the interface is fine, check the outbound prefix list.
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Ticket 5: the best path will not install
R1#show ip bgp rib-failure Network Next Hop RIB-failure RIB-NH Matches 203.0.113.0/24 10.255.0.2 Higher admin distance n/a
Show the cause
iBGP has an administrative distance of 200. Another source, such as a static or IGP route to the same prefix with a lower distance, wins the routing table. Remove the other route or change its distance if BGP should carry the traffic.
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Check your method
A session is Established but a prefix is not on the neighbour. Which command on the sender is the best first check?
FDE5 appears in a notification message. What do you do first?
A network statement is present but the prefix is not advertised. What is the likely reason?