Troubleshooting BGP
3 important questions on Troubleshooting BGP
What command can be used initially to verify BGP Neighbors?
Show bgp ipv4 unicast summary
What are some of the reasons a BGP neighborship might not form?
- Interface down
- Layer 3 connectivity broken
- Path to neighbor is through default route
- Neighbor does not have route to local router
- Incorrect neighbor statement. (IP Address and AS Number)
- ACLs blocking TCP 179
- BGP Packets sourced from wrong IP address
- TTL of BGP packet expires.
- Mismatched authentication
- Misconfigured peer group
- wrongly set timers
What are common reasons BGP Routes are missing from either the BGP Table or the Routing Table?
- Missing or bad network mask command
- Next-hop router not reachable
- BGP Split-horizon rule (Route learned from iBGP peer is not shared with other iBGP peer)
- Better source of information.
- Route filtering
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