PSN MTU problem?


bruce@think.com
Sat, 21 Feb 87 07:16:50 EST


Oh, I forgot to mention another problem which I first noticed last weekend.

We are unable to send segments to SRI-NIC.ARPA of size MTU. This time
NIC is the only host with which I have observed the problem. If I kludge
our tcp to negotiate a slightly smaller MSS, everything works fine.

On this end, we appear to be getting RFMNs from the long packet, but
NIC evidently isn't seeing it. The connection stays alive: we
retransmit the long packet, and they retransmit the previous ack.

This is not the standard 4.2/4.3 driver bug of not allocating buffers
at least one greater than MTU. That was fixed long ago. But the
symptoms are exactly the same. This is a NEW problem, and we haven't
changed any tcp/ip code here recently.

Evidently we can RECEIVE mtu-sized packets from the NIC.

--Bruce Nemnich, Thinking Machines Corporation, Cambridge, MA
  bruce@think.com, seismo!think!bruce, bjn@mitvma.bitnet; +1 617 876 1111



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