Re: IPv6 payload length check?

On 04-Feb-20 20:43, Aitken, Paul wrote:
> Thanks Eric.
> 
> In this case the packet is *not* larger than the MTU of the outgoing link. Rather a packet has been received (or possibly generated locally) with an IPv6 payload length greater than the link layer frame size.

'generated locally' would surely be a coding bug (probably in the socket API), since such a case should simply be impossible. Either the packet would have been fragmented or IPV6_DONTFRAG is set and the send() will fail. In any case it wouldn't be a protocol issue.

> Probably this packet should not be forwarded. However, I couldn't find anything to say that it's invalid.

I don't see a fast-path switch checking for this condition, so I think it can only be detected at the final destination, as others have said. But it seems like an implementation issue, not part of a protocol spec.

   Brian

> 
> Thanks,
> P.
> 
> 
> On 03/02/2020 22:05, Erik Kline wrote:
>> Interestingly, 8200 contains this text in the Routing Header section (4.4):
>>
>> """
>>    If, after processing a Routing header of a received packet, an
>>    intermediate node determines that the packet is to be forwarded onto
>>    a link whose link MTU is less than the size of the packet, the node
>>    must discard the packet and send an ICMP Packet Too Big message to
>>    the packet's Source Address.
>> """
>>
>> Really that text would seem to apply even if a routing header is absent.  4443 on PTBs (3.2) has the text you might be looking for:
>>
>> """
>>    A Packet Too Big MUST be sent by a router in response to a packet
>>    that it cannot forward because the packet is larger than the MTU of
>>    the outgoing link.
>> """
>>
>> On Mon, Feb 3, 2020 at 7:31 AM Aitken, Paul <paul.aitken@intl.att.com <mailto:paul.aitken@intl.att.com>> wrote:
>>
>>     Can anyone point me to a standards reference for the check to validate
>>     that the IPv6 payload length is less than or equal to the link layer
>>     frame size upon forwarding a packet?
>>
>>     Thanks,
>>     Paul
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