Le 3 août 09 à 13:54, Lars Eggert a écrit :
Hi,
On 2009-8-3, at 13:18, Rémi Després wrote:
In view of the various arguments made, here is IMHO a good
combination:
...
- IPv6 hosts MAY accept UDP datagrams with zero checksum.
I see no reason why allowing a UDP checksum of zero for router-to-
router tunnels under specific circumstances (existence of a payload
checksum), which is what we've been discussing for AMT and LISP,
motivates *any* changes for the host. As far as hosts as concerned,
nothing changes with regards to RFC2460.
- IPv6 hosts that accept zero-checksum UDP datagrams MAY restrict
this tolerance to remote hosts whose IPv6 addresses include an IPv4
mapped address.
(Thus no new tolerance is introduced for IPv6 hosts.)
Since there is no IP header checksum in IPv6, these IP addresses
can be corrupted, and so this check may fail.
If a host may receive receive a zero-checksum UDP datagram destined
to another host, this is acceptable because:
- Probability of this happening is very low (with link layer
checksums etc.).
- It is even more UNLIKELY that the source address and the two ports
of the datagram match those of an existing connection (connection
where, in addition, such datagrams must be accepted).
- If this nevertheless happens, the harm must be limited because of
the application nature. (For example, an application that accepts
queries in unchecked datagrams may receive an extra query without
significant consequence).
If in charge of an IPv6 TCP/IP stack (which I am not), I would ensure
that, although it never sends zero-checksum UDP datagrams, it does
accept to receive them.
Similarly, if in charge of of an SIIT (which I am not either), I
would ensure that rather than discarding IPv4 zero-checksum datagrams
it forwards them with its zero checksum.
This being said, it's up to people in charge to decide. (I don't care
very much. Efforts to have IPv6 end-to-end rapidly deployed are IMHO
more important than efforts to keep IPv4-only environments work as
well as if they would be dual stack.)
Regards,
RD
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