re: TCP maximum segment size determination


Craig Partridge (craig@NNSC.NSF.NET)
Tue, 10 Nov 87 10:13:22 -0500


Bruce,

    Last week I volunteered at the IETF meeting to write a proposal for
just such an IP option. You should see it within a couple of weeks
(seeing it implemented may take a while longer...)

    By the way, the scheme is sound even if the path changes if you
treat the IP option and the TCP MSS values as distinct.

    I.e. in the TCP MSS you should advertise the maximum segment
size you wish to accept and the remote end should keep this value
and separately keep track of what IP reports. You would use the minimum
of the two MSS's reported when sending. Then if you get an indication
that the route has changed (such as an ICMP redirect), you can send the
IP option again, and update the effective MSS (up or down). There's
still the problem of packets following different paths -- this may
have a solution but I'm still looking for something that doesn't feel
like a kludge of a three way handshake.

Craig



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