[Babel-users] MTU based routing for tunnel based babel networks?

[Daniel Gröber]

On Tue, Jul 18, 2023 at 03:37:14PM -0700, David Schinazi wrote:
> [ ... an hour passes by with this email half written ... ]
> 
> Oh, and in the meantime Juliusz just went ahead and implemented probe-mtu.
> Nicely done, sir! Looking at the PR it validates that the kernel-provided
> MTU gets through the network. I wonder if that breaks popular tunnel
> implementations today, as I suspect many don't set that correctly.

Ha, good thing you mentioned it I was just about to go back to patch
writing.

Interesting approach. IPV6_DONTFRAG is (again) not documented in ipv6(7) so
I had no idea this exists :)

FYI: From looking at the linux code it looks like it's possible to set
IPV6_DONTFRAG per-sendmsg() call (in the cmsg field, see
ip6_datagram_send_ctl() in linux) so this could also be a per-interface
option.

Awesome work Juliusz!

--Daniel