I have a question wrt RFC 1981 (path MTU discovery for IPv6). The RFC
says in Section 4. as follows:
Note: A node may receive a Packet Too Big message reporting a
next-hop MTU that is less than the IPv6 minimum link MTU. In that
case, the node is not required to reduce the size of subsequent
packets sent on the path to less than the IPv6 minimun link MTU,
but rather must include a Fragment header in those packets [IPv6-
SPEC].
RFC 2460 has a related text (in Section 5):
In response to an IPv6 packet that is sent to an IPv4 destination
(i.e., a packet that undergoes translation from IPv6 to IPv4), the
originating IPv6 node may receive an ICMP Packet Too Big message
reporting a Next-Hop MTU less than 1280. In that case, the IPv6 node
is not required to reduce the size of subsequent packets to less than
1280, but must include a Fragment header in those packets so that the
IPv6-to-IPv4 translating router can obtain a suitable Identification
value to use in resulting IPv4 fragments. ...
In my understanding, the only "translating router" that needs the
indication of the fragment header is an SIIT (or similar) translation
router. In fact, neither NAT-PT (RFC 2766) nor TCP-relay (RFC 3142)
needs the indication.
So my questions are:
- is my understanding correct?
- if so, is it allowed for a host not implementing SIIT client side to
ignore the requirement to insert the fragment header upon receiving
an ICMPv6 too big message with an MTU less than 1280?
JINMEI, Tatuya
Communication Platform Lab.
Corporate R&D Center, Toshiba Corp.
[EMAIL PROTECTED]
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