RE: Sh IP BGP Sum - T/S the BGP neighbors.

From: Devi Mallampalli (Devi.Mallampalli@chubb.com.au)
Date: Wed Jun 23 2004 - 03:14:41 GMT-3

Thanks for your feedback, James.

I asked this Q because the other day when I had trouble in bringing
couple of neighbors up during a lab practice , I have noticed that one
neighbor in Q is struck in "Active " state and I found that she is not
reachable (I can not ping it). Then that I had to go to L2 & L3 issues
and make sure she is reachable via TCP.

Meanwhile I was clearing both "ip route table" as well as "IP bgp table"
and waited for 2 or 3 minutes each. But as soon as I fixed that
neighbor's reachability issue, neighbor came on line with in sh ip bgp
sum table.

And the second neighbor was struck in "Idle state". Immediately I found
that node is reachable via IP , but still struck in to "Idle state".
After further analysis , I have realized that I have mentioned a wrong
remote-as on that neighbor's prefix.

Devi.

-----Original Message-----
From: James [mailto:james@towardex.com]
Sent: Wednesday, 23 June 2004 4:04 PM
To: Devi Mallampalli
Cc: ccielab@groupstudy.com
Subject: Re: Sh IP BGP Sum - T/S the BGP neighbors.

if i am thinking correctly, the bgp session is managed by the Finite
State Machine (FSM), which transitions following states until bgp TCP
connection is established between the peers, in following order:

1. Idle - router waits random time before attempting TCP connect 2.
Connect - attempting tcp connection to remote peer 3. Active -
connection timedout? wait random time, then go back to step 2. 4.
OpenSent - connection is opening. 5. Established - session is up 6. Any
Number - session is established and number of bgp prefixes received.

i don't exactly renumber all steps of the FSM, so above may not be 100%
accurate, but you get the idea..

so speaking in english, ifyou see Active, your session is down. most
likely
b/c connection is being rejected at one of the routers, or connection is
being timed out or other fatal errors preventing the peering to start.

hope this helps! :)

-James 

-- 
James Jun                                            TowardEX
Technologies, Inc.
Technical Lead                        Network Design, Consulting, IT
Outsourcing
james@towardex.com                  Boston-based Colocation & Bandwidth
Services
cell: 1(978)-394-2867           web: http://www.towardex.com , noc:
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On Wed, Jun 23, 2004 at 03:47:42PM +1000, Devi Mallampalli wrote:
> As part of trouble shooting BGP neighbor relationship problems , Am I 
> safe to think that when ever I do not see any "number" under last 
> column of "State/PfxRcd" (with sh ip bgp sum command) and that section

> shows me that peer is under , "Active" state , it means that I do not 
> have IP reachability problem between peers.
> &
> "Idle" state , it means that I do have IP reachability , but I have
some
> sort of configuration problem  under BGP process , i.e. with my
> remote-peer N/W prefix mentioning under BGP process or specifying a
> wrong AS number.
> Thanks for any verification.
> Devi.
> 
> 
> 
> 
> 
> 
> 
> 
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