[190711] in North American Network Operators' Group
Re: MTU
daemon@ATHENA.MIT.EDU (Phil Rosenthal)
Fri Jul 22 14:20:47 2016
X-Original-To: nanog@nanog.org
From: Phil Rosenthal <pr@isprime.com>
In-Reply-To: <520e997e-9c83-3d1c-b99b-b818e3ea3b16@Janoszka.pl>
Date: Fri, 22 Jul 2016 14:20:41 -0400
To: Grzegorz Janoszka <Grzegorz@Janoszka.pl>
Cc: nanog@nanog.org
Errors-To: nanog-bounces@nanog.org
> On Jul 22, 2016, at 1:37 PM, Grzegorz Janoszka <Grzegorz@Janoszka.pl> =
wrote:
> What I noticed a few years ago was that BGP convergence time was =
faster with higher MTU.
> Full BGP table load took twice less time on MTU 9192 than on 1500.
> Of course BGP has to be allowed to use higher MTU.
>=20
> Anyone else observed something similar?
I have read about others experiencing this, and did some testing a few =
months back -- my experience was that for low latency links, there was a =
measurable but not huge difference. For high latency links, with Juniper =
anyway, there was a very negligible difference, because the TCP Window =
size is hard-coded at something small (16384?), so that ends up being =
the limit more than the tcp slow-start issues that MTU helps with.
With that said, we run MTU at >9000 on all of our transit links, and all =
of our internal links, with no problems. Make sure to do testing to send =
pings with do-not-fragment at the maximum size configured, and without =
do-not-fragment just slightly larger than the maximum size configured, =
to make sure that there are no mismatches on configuration due to vendor =
differences.
Best Regards,
-Phil Rosenthal=
