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Re: Issue 19 of draft-ietf-ipv6-node-requirements-05.txt



Thomas Narten wrote:

>>>>   Nodes MUST always be able to receive fragment headers. However, if it
>>>>   does not implement path MTU discovery it may not need to send
>>>>   fragment headers.  However, nodes that do not implement transmission
>>>>   of fragment headers need to impose a limitation to the payload size
>>>>   of layer 4 protocols.
>>>
>>>     
>>>This would seem inconsistent with the following wording in RFC 2460:
>>>
>>>    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.

Oops, yes.

>>So, this should be changed to:
> 
> 
>>	Nodes MUST always be able to send and receive fragment headers. (rest of
>>	the text deleted)
> 
> 
> how about:
> 
>  	Nodes MUST always be able to send and receive fragment
>  	headers. Note that even in the case where a sender does not
>  	implement or use Path MTU discovery [RFC 1981], the sender
>  	must still be prepared to send fragment headers, even for
>  	packets that are smaller than the minimal IPv6 link MTU of
>  	1280 octets. See Section 5 of [RFC 2460] for details.

Sounds good. Pekka Savola's slight modification of
this is OK, too.

--Jari






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