How to adjust TCP MSS on ASR9000 Tunnel-Interface?

[senpai]

I have read through the excellent post on TCP MSS Adjust on ASR9000 by Aleksandar Vidakovic. According to that post, to adjust MSS one must configure the hw-module location 0/0/CPU0 tcp-mss-adjust np 1 value <number> and then apply it on the corresponding interface which belongs in 0/0/CPU0.

Now my question is, how to apply this when its a Tunnel-Interface? If my guess is correct, I have to enable under the tunnel-ip the command 'ipv4 tcp-mss-adjust enable' and locate the exit interface the tunnel uses for its destination address and then apply the corresponding 'hw-module location 0/0/CPU0 tcp-mss-adjust np 1 value <number>' changing the location CPU which belongs to the exit interface. 

And then the tunnel MSS will be correctly adjusted when sending packets. Am I correct? or can anyone shed some light on how to adjust this on the tunnel interface.

Thanks

[nkarpysh · Accepted solution]

Correct,



The mss runs on a per npu bases, so you need to enable it on the tunnel and also define the value of the mss on the npu's that possibly could receive the tunnel traffic (whether it be before -> traffic going into the tunnel, or after decap -> coming out of the tunnel).

[nkarpysh]

Thanks for your query. i used your wording (hope you dont mind) and updated the original Aleks's article with those.
:)
Niko

[senpai]

hah you're welcome. Never knew this query would help update an excellent post on MSS. everyone reaps the benefit. appreciate your reply thanks :)