>> Sorry, I wasn't clear. IP requires every link to have a well-defined
>> MTU: all the nodes connected to a link must agree on the link's MTU.
> I don't think that can be true either. PMTU can vary and paths can be
> asymmetric so two nodes could very well see different MTUs across the
> internet. There's just not many ASen that run with less than 1500 MTU :)
I'm not speaking about PMTU. I'm speaking about link MTU.
> Do you have a referece for this "MTU well-definedness" criteria, I don't
> think I ever heard of this.
RFC 2460: "link MTU - the maximum transmission unit, i.e., maximum packet
size in octets, that can be conveyed over a link."
RFC 4861: "All nodes on a link must use the same MTU (or Maximum Receive
Unit) in order for multicast to work properly."
> Wireguard drops packets when they exceed the underlay network's MTU.
> this happens no PTB ICMP errors are generated by wireguard inside the
> tunnel,
If true, that's very surprising, and looks to me like a bug in Wireguard.
But yeah, I'll add an option to probe for MTU on each Hello.
-- Juliusz
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