What do if a tool small link MTU is detected?

[mirjak]

I think there are two option here, 1) close/deny the connect request, and 2) use streams instead. I think we should consider both option, especially given stream are just there to use.

[tfpauly]

Isn't this a dup of #45? That's fixed with #60.

I guess the text could be generalized to talk about more than just IPv6 MTU issues.

[gloinul]

Isn't this a dup of #45? That's fixed with #60.

No, this aspect on what you do when the MTU required is not present is not resolved by that PR. I would note that closing gives the endpoints one experience that is likely easier to handle in implementation and do avoid the issue with reordering and the varying packet treatment that moving to stream would result.

[DavidSchinazi]

I would suggest adding a sentence saying that if an endpoint realizes that the IPv6 tunnel MTU goes lower than 1280, then it MUST close the stream.

[ekinnear]

IETF 114: Note that if something happens and your MTU gets smaller, you may need to destroy that link. Potentially make this option a SHOULD do PMTUD, otherwise you could end up in a situation where you're not a compliant IPv6 tunnel.

Proposal:

If you are sending the IP packets over datagrams and you detect that the path MTU is no longer sufficient, you MUST close the stream because you're in violation of the RFC.