> RFC 2460 section 5 last paragraph says:
> 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. Note that this means the
> payload may have to be reduced to 1232 octets (1280 minus
> 40 for the
> IPv6 header and 8 for the Fragment header), and smaller still if
> additional extension headers are used.
>
> Does that answer your question?
I know about that, but my question is whether i need to add a frag header
everytime path mtu discovery fails (i.e. i get some mtu value < 1280 from
the pkt too big message). The only case when i think pmtu discovery can fail
is in the "translator scenario" (do you know of any other cases??). But note
that RFC 2460 says that we need to add a frag header "In response to an IPv6
packet that is sent to an IPv4 destination....". I think it should be
something like "Add a frag header when pmtu discovery to a destination
fails" since we cannot distinguish the case when path mtu discovery is done
from ipv6 to ipv4.
regards,
imran
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