Re: UDP zero checksums and v4 to v6 translators

[Christopher Morrow <christopher.morrow at gmail.com>]

On Tue, Jul 28, 2009 at 3:29 AM, Francis
Dupont<Francis.Dupont at fdupont.fr> wrote:
>  In your previous mail you wrote:
>
>   Thoughts?
>
> => I am strongly against changing all IPv6 implementations.
> IMHO the simplest solution is to drop UDP packets with zero checksums
> (as far as I know all IPv4 implementations use non-zero checksums
> per default and some UDP applications, for instance DNS, work far
> better with non-zero checksums. BTW it is an easy condition to check
> in firewalls).

Out of curiosity, what's the signal back to the sender that his/her
packet was dropped?? NFS (in some implementations) doesn't checksum
UDP packets, DNS doesn't, there are quite a few things that don't
checksum UDP packets.

Simply dropping packets on the floor isn't polite. Dropping them and
notifying (icmp <somethingbadhappenedhere>) is also hard to deal with
since users can't force udp checksums to happen (per
application/stack) and there's not a clear (aside from application
failure) idea to the user that something isn't working.

If you choose to drop the packet tell the sender that it happened
(port-unreachable or something along those lines, still the wrong
semantics though), I believe you should accept and correct the
checksum issue though in the end, it's the only proper path.

-Chris