CCNP - ENTERPRISE - BGP - Neighbor States

When establishing neighbor sessions, BGP transitions through a number of states. These are:

1. IDLE - router is searching routing table to see whether a route exists to the neighbor*
2. CONNECT - Router found a route to the neighbor and 3 way TCP handshake is complete
3. Open Sent - Open msg with parameters for BGP session is sent
4. Open Confirm  - Router received an agreement on the parameters to establish a session. Alternatively, the router enters ACTIVE state is not responds is received to the Open Sent msg
5. ESTABLISHED - peering established, routing begins.

To view this activity you can use the debug options to see the process in action.

Configuration:

R1#debug ip bgp all

!

R1#debug ip bgp events

!

Remember, a debug is processor intensive so remove the debug once you are finished:

R1#undebug all 

OR

R1#u all 

!

*I can't remember if I've already stated this but in the UK the word is spelt NEIGHBOUR. For consistency with Cisco IOS commands I'm spelling it NEIGHBOR when I need to use the word. Thought I'd just clarify that as I'm not some dumb ass that can't spel. ...erm...