BGP startup

[martin_lx1980]

I want to check how BGP connection is built between peers.so first I write below two commands for one of peer

Router bgp 1

Neighbor 192.168.12.2 remote-as 1

I see some information from debug output at once

*Mar 1 00:17:49.447: BGP: 192.168.12.2 went from Idle to Active

*Mar 1 00:17:49.455: BGP: 192.168.12.2 open active delayed 29431ms (35000ms max, 28% jitter)

First question: why BGP status goes from idle to active even if I don’t start BGP on the remote peer? there is not a direct way from idle to active in BGP FSM

Second question: you could see that (35000ms max, 28% jitter). what is the timer and how does this timer work?

Thanks a lot

Martin

[Eugene Khabarov]

Hi! BGP goes to Active state immediately after IDLE because router is trying to setup tcp connection to neighboring device even if there is no configuration on neigboor. You can view the full process by enabling debug ip bgp and debug ip tcp transactions

In other words - router goes from connect state very quickly.

About second question:

I think the explanation is that router sets the ConnectRetry timer and cannot attempt to restart BGP until the timer expires. By default it is 120 seconds or 120000 ms long. Also by RFC 4271 some kind of variance called jitter added to this value.

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