Unformatted text preview: e:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_conn.htm (17 of 37) [12/09/2001 14.47.16] Chapter 18. TCP Connection Establishment and Termination incarnation plus 128,000. The appendix of RFC 1185 [Jacobson, Braden, and Zhang 1990]
shows the pitfalls still possible with this technique.
This implementation feature lets a client and server continually reuse the same port number at
each end for successive incarnations of the same connection, but only if the server does the
active close. We'll see another example of this 2MSL wait condition in Figure 27.8, with FTP.
See Exercise 18.5 also.
Quiet Time Concept
The 2MSL wait provides protection against delayed segments from an earlier incarnation of a
connection from being interpreted as part of a new connection that uses the same local and
foreign IP addresses and port numbers. But this works only if a host with connections in the
2MSL wait does not crash.
What if a host with ports in the 2MSL wait crashes, reboots within MSL seconds, and
immediately establishes new connections using the same local and foreign IP addresses and
port numbers corresponding to the local ports that were in the 2MSL wait before the crash? In
this scenario, delayed segments from the connections that existed before the crash can be
misinterpreted as belonging to the new connections created after the reboot. This can happen
regardless of how the initial sequence number is chosen after the reboot.
To protect against this scenario, RFC 793 states that TCP should not create any connections for
MSL seconds after rebooting. This is called the quiet time.
Few implementations abide by this since most hosts take longer than MSL seconds to reboot after a crash. FIN WAIT 2 State
In the FIN_WAIT_2 state we have sent our FIN and the other end has acknowledged it. Unless
we have done a half-close, we are waiting for the application on the other end to recognize that
it has received an end-of-file notification and close its end of the connection, which sends us a
FIN. Only when the process at the other en...
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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