On 2009-07-30 13:35, Christian Huitema wrote:
>>> What happened to being conservative with what we send and permissive
>> with what we receive?
>>> It seems that the direct application should be:
>>>
>>> 1) Be conservative: hosts should not send UDP packets with null
>> checksums.
>>> 2) Permissive: gateways who receive UDP packets with null checksum
>> should compute a checksum based on the received bytes, and then forward
>> the packet.
>>> I understand there may be resource limits on gateways, and that the
>> UDP checksum compute requirement might throw the packet back to some
>> kind of slow path, with potential packet loss due to congestion. But
>> that's way better than a black hole.
>>
>> The problem is *fragmented* IPv4 UDP packets with zero checksum; the
>> translator would have to reassemble them.
>
> The fragmentation issue is different from the zero-checksum issue. Many IPv4
> NAT drop fragmented packets already. They rely on port numbers to find the
> mappings, fragments don't carry port numbers, so fragments get dropped.
> Application developers ought to know by now that sending large UDP packets
> over IPv4 is problematic.
BEHAVE's issue is to decide whether dropping them is
an acceptable recommendation for v4->v6 translators.
Brian
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