[c-nsp] MTU and PMTUD

[Saku Ytti]

On Thu, 8 Dec 2022 at 11:40, Marcin Kurek <md.kurek at gmail.com> wrote:
>
> >  https://www.rfc-editor.org/rfc/rfc8654.html
>
> Thanks!
>
> > But it was [8936, 1240].min - so it was 'negotiated' here to the
> > smallest? If you change the 8936 end to 1239, then that will be used,
> > regardless who starts it.
>
> Yes, but why would XR advertise 1240 if I'm using 'tcp mss 8936' for that neighbor?
> Initially I thought that the whole point of this command is to set MSS to a fixed value of our choice.

I may have misunderstood you. Ddi you have 8936 configured on both
ends? I thought you had only 8936 on the CSR.

How I understood it:

*Dec  8 11:17:15.453: TCP0: Connection to 12.0.0.7:179, advertising MSS 8936
*Dec  8 11:17:15.456: TCP: tcb 7FFB9A6D64C0 connection to
12.0.0.7:179, peer MSS 1240, MSS is 1240

Local 12.0.0.13 CSR is advertising 8936 to remote 12.0.0.7
Remote 12.0.0.7 is advertising 1240
We settle to 1240

I guess you are saying the remote 12.0.0.7 is as well configured to
8936? Then I agree, I wouldn't expect that, and can't explain it.
Almost sounds like a bug where the configuration command is only read
when IOS-XR establishes the connection, but not when it receives it?

-- 
  ++ytti