potentially disallowing IP fragmentation on wg packets, and handling routing loops better

[Nico Schottelius]

Hello,

so given that fragmentation is disallowed the PMTU discovery always
needs to work and the wireguard MTU needs to be correctly adjusted.

Speaking of a DC situation, I think this might be tricky. Imagine the
following situation:

- endhost A has an MTU of 9k. PMTU 9k. wg 8920.
- the path changes, the PMTU reduces to 1.5k (this is something we see
 happening from time to time)
- How is the wg MTU adjusted in this situation?

And to clarify: with disallowing IP frag, you are obviously only
referring to the outter transport. Within the tunnels, IPv6 and IPv6
packets can still be fragmented, so application operation is not really
affected.

Interesting approach, I am not really sure if realisticly feasible,
especially when thinking about long range/low bandwidth media where
you'd basically say "wg cannot do IPv6 on these mediums". Satelite
systems should probably work fine, I am more concerned about mesh
networks, in which wg is quite popular already.

Cheers,

Nico

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