<Keepalives are temporarily in throttle due to closed TCP window>

Tue Sep 15 20:49:57 UTC 2009

>Take a look at the interfaces over which the peering session runs, at
both ends.
>I.e., is this the only BGP session *over that interface*, for the local
box?

You are going to find this even more strange.  I have two routers that
are communicating over the same transport medium and are actually in the
same rack. One router is a Cisco 7606 which has an IBGP session
established with my Cisco 6509.  Both equipment have Sup-7203bxls 1 Gig
of memory. Ironically from the 6509's perspective, I cannot seem to
maintain a session with my 7206VXR which has two directly connected
DS-3s.  In order for my 6509 to establish an IBGP session with my 7606,
it has to go through the 7206 VXR.  Crazy right?

Yeah I can already this is going to be a *War Story* as you said it. :)

-----Original Message-----
From: Brian Dickson [mailto:Brian.Dickson at concertia.com] 
Sent: Tuesday, September 15, 2009 3:40 PM
To: Mikael Abrahamsson; Michael Ruiz
Cc: nanog at nanog.org
Subject: RE: <Keepalives are temporarily in throttle due to closed TCP
window>

And more specifically, possibly an interface MTU (or ip mtu, I forget
which).

If there is a mismatch between ends of a link, in one direction,
MTU-sized packets get sent, and the other end sees those as "giants".

I've seen situations where the MTU is calculated incorrectly, when using
some technology that adds a few bytes (e.g. VLAN tags, MPLS tags, etc.).

On Cisco boxes, when talking to other Cisco boxes, even.

Take a look at the interfaces over which the peering session runs, at
both ends.
I.e., is this the only BGP session *over that interface*, for the local
box?

(It might not be the end you think it's at, BTW.)

Oh, and if you find something, please, let us know.
War stories make for great bar BOFs at NANOG meetings. :-)

Brian

-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike at swm.pp.se] 
Sent: September-14-09 2:39 PM
To: Michael Ruiz
Cc: nanog at nanog.org
Subject: Re: <Keepalives are temporarily in throttle due to closed TCP
window>

On Mon, 14 Sep 2009, Michael Ruiz wrote:

> I am having difficulty maintaining my BGP session from my 6509 with
> Sup-7203bxls to a 7206 VXR NPE-400.  The session bounces every 3
> minutes.  I do have other IBGP sessions that are established with no
> problems, however, this is the only IBGP peer that is bouncing
> regularly.
>
> What does exactly the message mean and how do I stabilize this?  Any
> help will be appreciated.

This is most likely an MTU problem. Your SYN/SYN+ACK goes thru, but then

the first fullsize MSS packet is sent, and it's not getting to the 
destination. 3 minutes is the dead timer for keepalives, which are not 
getting thru either because of the stalled TCP session.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se