Caching learned MSS/MTU values

Hannes Frederic Sowa hannes at
Fri Oct 18 18:45:43 CEST 2013


On Fri, Oct 18, 2013 at 04:35:39PM +0000, Templin, Fred L wrote:
> > There is basis support for mtu probing for tcp. It is currently
> > deactivated by
> > default: cat /proc/sys/net/ipv4/tcp_mtu_probing => 0
> > 
> > Guess it had not the seen the testing it needs to activate it by
> > default.
> Yes, I had heard that there was an off-by-default linux implementation
> of RFC4821. I also heard that it was not yet fully compliant to the
> spec, but that was a while ago now and it may have gotten better by now?

Going through the git logs it does not seem to get a lot of commits. Maybe it
is just stable, I don't know. I'll activate it on my boxes now to see if
something breaks.

The committed patch droped the note that it is not fully spec compliant but
seems to be based on the -05 draft.

> > I still have to take a closer look at SEAL. Thanks for the reminder. ;)
> Sure. I have recently published an alpha linux implementation of SEAL:
> It is still in early phases and does not yet fully implement the spec
> but does implement the core RFC4821 path MTU probing and fragmentation
> requirements for several different varieties of tunnels. The code is
> also quite ugly, and I would welcome any help on cleaning it up and/or
> implementing more features in the spec.

Oh, that is interesting. I'll have a look at the weekend.



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