Ultrix 1.2 and unacceptable tcp packets

Edward J Cetron (cetron@utah-cs.arpa)
Mon, 15 Sep 86 15:23:12 MDT

After hacking with the Tek tcp/ip package to add keep-alive (or probe-alive
as the case may be) support, I found the following behaviour from two Ultrix

        line sits idle for x length of time (so snd.nxt = snd.una = Ultrix
        Tek tcp/ip sends a packet designed to be unacceptable in order to force
                a response (as documented in the mil-std and rfc for tcp). This
                packet has seg.seq = snd.nxt-1 and seg.ack = rcv.nxt-1
                which is obviously unacceptable and should force and ack with
                the proper counters.

        The Ultrix site receives the packet, and promptly drops it off of the
                face of the earth (though apparently reading the code it does
                use it to update the window...)

Am I missing something or is this indeed non-compliant? All of the 4.2bsd and
4.3 bsd sites handle this fine... I know what is different between the 4.3bsd
and the Ultrix code but before I fix it myself, I want to be sure I haven't
overlooked something and/or that other Ultrix sites have noticed this same




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