On 06/ 3/10 01:03 AM, JP Vasseur wrote:
Just a clarification, ROLL is not tied to 15.4 and could run on many
other media with various MTU.
That was what I feared.
We can use the outlined approach as long as we can require such media to
support a MTU for IP packets that is slightly larger than 1280.
Thus we'd need a maximum size for the amount the ROLL ingress would add
to the packet (RH4 and the HBH), and then require that the ROLL links
support at least 1280 plus that max. Essentially a ROLL_MIN_MTU.
That would ensure that the ROLL ingress would never need to fragment a
1280 byte packet. And for packets larger than 1280, the rewriting of the
ICMP errors at the ROLL boundary would make path MTU discovery work.
But if we can't mandate such a ROLL_MIN_MTU, then the sensible approach
would seem to be to do IP in IP encapsulation at the ROLL ingress.
Erik
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