Re: [tsvwg] UDP Options: on forcing the use of UDP CS=0 in connection with FRAG+LITE

["C. M. Heard" <[e-mail]>]

On Sat, Jun 29, 2019 at 7:58 AM Joe Touch wrote:
>
> See sec 8.1, which incorporates rfc 6936:
>
>          As an exception to the default behavior, protocols that use UDP
>          as a tunnel encapsulation may enable zero-checksum mode for a
>          specific port (or set of ports) for sending and/or receiving.
>          Any node implementing zero-checksum mode must follow the
>          requirements specified in "Applicability Statement for the Use
>          of IPv6 UDP Datagrams with Zero Checksums" [RFC6936].
>
> Frag is a kind of such a tunnel because it adds its own reassembly CS.

I'll agree that FRAG+LITE with UDP CS=0 does conform to the requirements
in RFC 6936 Sections 4 and 5 because it includes a reassembly CS.

> But that also means middleboxes should allow relaying these since 6936
> was passed.

Yes. middleboxes are ***supposed*** to do that. But the empirical data
that we have says that in a significant number of cases (affecting 26%-36%
of the paths) they do not.

It's possible that the situation will improve in the future, but given
that it has not improved enough to make UDP CS=0 useable in other than
controlled environments, I don't think it's a good idea to propose its
use when we have an alternative that avoid UDP CS=0 that is no more
complex to implement.

Mike Heard