Troubleshooting BGP

The new focus is of the R&S exam is troubleshooting. And for some reason this is seen as a new topic to study and as a result feared. It is vital to understand why troubleshooting was added to the lab, and why it will possibly be added to other tracks.  Anybody can apply vanilla configs, provided it is done without error, in the correct order, and by avoiding the question pitfalls.

Troubleshooting was introduced by Cisco to give the CCIE certification that edge it needs to seperate the guys that really understand the technologies and those that just learned to configure labs. Troubleshooting is thus NOT a new section! If you understand know each technology, understand its it building blocks, processes and states, troubleshooting should be nothing ‘new’.

That said, once you understand the work, drafting a troubleshooting methodology per technology should be fairly straight forward. A detailed troubleshooting approach is included in each chapter of the Routing-Bits Handbooks.

(Note ‘{ }’ curl-brackets indicate replaceable values, the rest is regex)

Troubleshooting BGP session start-up problems

1- Are you seeing the expected neighbors in a NON ‘idle’ or ‘active’ state?
#sh ip bgp summary

2- Is a sourced telnet to the neighbor address working?
#telnet {peer-ip} 179 /source {src-int-ip}

3- Confirm if the configuration is correct and matching to neighbors configuration?
#sh run | b router bgp

4- If eBGP, is the neighbor directly connected? (Should be 1 hop in the trace)
4.1- If not directly connected is multihop configured?
#trace {peer-ip} source {src-int-ip}
#sh run | i {peer-ip}.*ebgp-multihop

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