[j-nsp] mx960 to mx960 via ciena 6500 - mtu smaller in the middle

[James Bensley]

On 17 April 2018 at 11:57, Gert Doering <gert at greenie.muc.de> wrote:
> Hi,
>
> On Tue, Apr 17, 2018 at 12:34:18PM +0300, Saku Ytti wrote:
>> On 17 April 2018 at 11:25, James Bensley <jwbensley at gmail.com> wrote:
>>
>> > Also you say you have OSPF and LDP up but if you bring up BGP over
>> > this link you may have issues. BGP packs UPDATE messages up to the TCP
>> > MSS (derived from the link MTU). If you are carrying the full table
>>
>> BGP messages are limited to 4096.
>
> Which does not stop TCP from coalescing two messages into one 8 kbyte packet.
>
> (As in "I have had a link that was transported over someone else's packet
> network, and when they re-routed in an outage, I lost 8 bytes MTU,
> resulting in TCP failing across a 9200-minus-8-byte-link...")

This is what I have observed on IOS, UPDATES are packed to the TCP
MCC. Not sure if it's the case for Junos too but I simply wouldn't
risk it.

Cheers,
James.