RE: [BEHAVE] UDP zero checksums and v4 to v6 translators

[Christian Huitema <huitema at microsoft.com>]

> BEHAVE's issue is to decide whether dropping them is
> an acceptable recommendation for v4->v6 translators.

So there are really several cases

1) No fragmentation:
        1a) Checksum correct, => No issue, just translate.
        1b) Zero checksum, no fragmentation => Should compute the checksum, then translate
        1c) Invalid checksum => Should drop.

2) Fragmentation:
        2a) Enough resource to reassemble the packet:
                reassemble;
                2a1) checksum present & correct => translate
                2a2) zero checksum => Should compute the checksum, then translate
                2a3) invalid checksum => drop
        2b) Not enough resource to translate the packet:
                MAY drop the packet.

The main problem in case 2b is, what to do with the next packets. If the relay cannot perform reassembly, it will not know whether subsequent segments follow an initial segment with checksum, or without. There may be ways to pipeline segments, but that does not seem realistic.

-- Christian Huitema