Problems with 4.2 BSD TCP and half-o

[jbn at wdl1.UUCP]

     This looks sound by my copy of MIL-STD-1778.   The TCP concept here
is that when A is in a synchronized state and gets a segment outside
the window, it sends a current ACK (i.e. a duplicate of A's last ACK).
See table XII, row 1, noting that in some copies of MIL-STD-1778 tables
XII and XIV were switched; the proper XII is the longer one.
This provides B with current sequence information.  So, if B is in
SYN SENT state, and gets an ACK that is not the one expected, because
it's talking to a half-dead connection at A, it sends an RST, per
table VIII, row 8.  Receipt of this RST by A will kill the connection
at A.  B will then retransmit its SYN, which will now establish a new
connection.  This is the famous ``three way handshake'' in action. 

					John Nagle
					Ford Aerospace and Communications Corp.