[c-nsp] BGP convergence with jumbo frames

[Tantsura, Jeff]

IP MTU ?

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Pete Kruckenberg
Sent: Monday, August 02, 2004 7:42 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] BGP convergence with jumbo frames

Spent some time recently trying to tune BGP to get convergence down as
far as possible. Noticed some peculiar behavior.

I'm running 12.0.28S on GSR12404 PRP-2.

Measuring from when the BGP session first opens, the time to transmit
the full (~128K routes) table from one router to another, across a
jumbo-frame (9000-bytes) GigE link, using 4-port ISE line cards (the
routers are about 20 miles apart over dark fiber).

I noticed that the xmit time decreases from ~ 35 seconds with a 536-byte
MSS to ~ 22 seconds with a 2500-byte MSS. 
>From there, stays about the same, until I get to 4000, when
it beings increasing dramatically until at 8636 bytes it takes over 2
minutes.

I had expected that larger frames would decrease the BGP converence
time. Why would the convergence time increase (and so significantly) as
the MSS increases?

Is there some tuning tweak I'm missing here?

Pete.


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