Cisco BGP Troubleshooting

Some times there is nothing better for trouble shooting that a nice process tree. Cisco has a great set of them here.

My favorite is “Troubleshoot missing routes”:

Always remember that when you check your filters that you are checking your prefix list AND your AS-path filters!
Issue the “show ip bgp sum” command to get the quick and dirty on your peers.
Then issue “show ip bgp nei X.X.X.X received-routes”. This will give you all the routes this peer is sending you, before they hit your filters.
Next issue “show ip bgp nei X.X.X.X routes”. These are the routes that have made it past your prefix list filters, but not necessarily your AS filters. If the route has the > by it, then it will make it to the route table, if it doesn’t, ensure that it passes the AS filter. Double check for prepending and such.