Re: Clarify SCTP max packet size.

On Jul 6, 2009, at 3:12 PM, David Laight wrote:

>
>> Tell Vendor B to learn to read (RFC 1122) before coming
>> back as well.  MTU must be configurable on an interface.
>
> The problem I see here, is that it is the path-mtu that
> has to be 1400, not in interface mtu.
> All you are likely to be able to do on 'B' is set the interface mtu.
>
> IIRC IP only requires 576 (or so) bytes, 1500 is the standard
> ethernet mtu, but for PPPoE the mtu is a few byte shorter (1492?).
> so if SCTP actually requires 1500 it will never work over PPPoE.
There is no requirement for an MTU to be at least 1500 bytes.
The point is that SCTP must not announce less then 1500 bytes in
the a_rwnd of the INIT and INIT_ACK. And the SCTP layer should be
able to receive packets of at 1500 bytes. If the lower layer
only supports less, then it does not affect this, since the
smaller packets are also supported.
>
> Any equipment attached to a physical ethernet cable that can't
> receive maximal length ethernet packets seems very non-conformant!
> (Using it probably requires that ALL systems on that network use
> the smaller mtu.)
>
> 	David
>
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