In some mail from Fernando Gont, sie said:
> The IPv4 minimum MTU is 68, and not 576. If you blindly send packets larger
> than 68 with the DF bit set, in the case there's an intermmediate with an
> MTU lower that 576, the connection will stall.
And I think you can safely say that if you see any packets trying to
indicate that the MTU of a link is "68" then you should ignore it.
This came up some years ago in discussion about ... hmm... I think it
was what made a good (or sensible) "fragmentation required" ICMP message.
Ignoring quenches as a problem, if you try to send 10K of data to a
box that has an MTU of 68, 1200+ packets are required vs less than 10
for an ethernet MTU. The problem is 1200 packets require a lot more
system time to send than 6 or 7. A different kind of DoS attack.
I think it is reasonable to say anyone trying to advertise an MTU less
than 576 has nefarious purposes in mind.
> The IPv4 minimum MTU is 68, and not 576. If you blindly send packets larger
> than 68 with the DF bit set, in the case there's an intermmediate with an
> MTU lower that 576, the connection will stall.
And I think you can safely say that if you see any packets trying to
indicate that the MTU of a link is "68" then you should ignore it.
This came up some years ago in discussion about ... hmm... I think it
was what made a good (or sensible) "fragmentation required" ICMP message.
Ignoring quenches as a problem, if you try to send 10K of data to a
box that has an MTU of 68, 1200+ packets are required vs less than 10
for an ethernet MTU. The problem is 1200 packets require a lot more
system time to send than 6 or 7. A different kind of DoS attack.
I think it is reasonable to say anyone trying to advertise an MTU less
than 576 has nefarious purposes in mind.
oh, IPv6 guarantees a min. MTU of 1280.
Lets just stop using IPv4 already.
Darren
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