Wednesday, September 8, 2010

BSCI - 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...

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