MTU

Fri Jul 22 18:35:14 UTC 2016

> On 22 Jul 2016, at 19:37, Grzegorz Janoszka <Grzegorz at Janoszka.pl> wrote:
> 
>> On 2016-07-22 15:57, William Herrin wrote:
>> On a link containing only routers, you can safely increase the MTU to
>> any mutually agreed value with these caveats:
> 
> 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.

Quite obvious thing - BGP by default on Cisco and Juniper will use up to max allowed 4k message per packet, which for typical unicast IPv4/v6 helps to pack all attributes with prefix. This not only improves  (lowers) CPU load on sending side but also on the receiving end and helps with routing convergence.

There was a draft to use up to 9k for BGP messaging, but I belive it's buried somewhere on the outside of town called "our current version RFC".

-- 
Łukasz Bromirski