Re: IPv6 payload length check?

On Tue, 4 Feb 2020, 18:43 Aitken, Paul, <paul.aitken@intl.att.com> 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.
>
> Probably this packet should not be forwarded.
>

It's better to forward it without checking.

These packets with this fault are going to be rare. Checking each and every
packet for this rare problem at each forwarding hop would impact forwarding
performance.

The fault with the packet will be detected at the final destination and
dealt with there.

However, I couldn't find anything to say that it's invalid.
>

When could it ever be valid?

With protocol specs, everything unspecified is implicitly invalid, because
it is out of specification or unspecified behaviour.

> 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>
> 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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