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Unformatted text preview: .* The first line for port 23 is the ESTABLISHED connection. All four elements of the local and
foreign address are filled in for this connection: the local IP address and port number, and the
foreign IP address and port number. The local IP address corresponds to the interface on which
the connection request arrived (the Ethernet interface, 126.96.36.199).
The end point in the LISTEN state is left alone. This is the end point that the concurrent server
uses to accept future connection requests. It is the TCP module in the kernel that creates the
new end point in the ESTABLISHED state, when the incoming connection request arrives and
is accepted. Also notice that the port number for the ESTABLISHED connection doesn't
change: it's 23, the same as the LISTEN end point.
We now initiate another Telnet client from the same client (slip) to this server. Here is the
relevant netstat output: Proto
0 SendForeign Address
188.8.131.52.23 184.108.40.206.1030 ESTABLISHED
220.127.116.11.23 18.104.22.168.1029 ESTABLISHED
0 file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_conn.htm (28 of 37) [12/09/2001 14.47.16] Chapter 18. TCP Connection Establishment and Termination tcp 0 0 *.23 *.* LISTEN We now have two ESTABLISHED connections from the same host to the same server. Both
have a local port number of 23. This is not a problem for TCP since the foreign port numbers
are different. They must be different because each of the Telnet clients uses an ephemeral port,
and the definition of an ephemeral port is one that is not currently in use on that host (slip).
This example reiterates that TCP demultiplexes incoming segments using all four values that
comprise the local and foreign addresses: destination IP address, destination port number,
source IP address, and source port number. TCP cannot determine which process gets an
incoming segment by looking at the destination port number only. Also, the only one of the
three end points at port 23 that will receive incoming connection requests is the one in the
LISTEN state. The end points in t...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12