[j-nsp] BGP Hold time expiry

[Kevin Oberman]

> Date: Fri, 19 Sep 2008 09:45:33 -0700 (PDT)
> From: "P.Narayana Swamy" <pnswamy2 at yahoo.com>
> Sender: juniper-nsp-bounces at puck.nether.net
> 
> Hi,
> The EBGP session failed between Juniper and other vendor with the
> following log in Juniper Chassis.  Juniper chassis sent the Hold timer
> expired Notification and ceased the session.  Could you please let me
> know the reason for this Holdtime expiry? Were there any TCP session
> failure or any Path MTU issues from the following log:

Looks a lot like an MTU mismatch. BGP does not do PMTU and sets do not
fragment, so the MTUs need to be the same on both ends. Things like VLAN
or tunneling can mess this up.

You can try capturing the traffic to confirm this. I use tcpdump (in the
shell as root) and move the output file to a box where I can run
wireshark on it. You will see the big frame being re-transmitted several
times. This is probably not really required, though.

The common symptom is that one end (the one with the larger MTU) will
get "stuck" with a message in the outbound queue that never gets
sent. This is visible in "sho bgp sum | grep peer-ip-address". The fifth
column is the one you will see freeze for a while and slowly grow as
keep-alives are added to the queue.

At that point, the keep-alives and other stuff is blocked in the output
queue and never gets sent. Finally, the session times out and you start
over. This is not 
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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