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Unformatted text preview: ed the window advertisements and type-of-service values.) file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (12 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol Figure 27.8 Data connection for two consecutive LIST commands.
The sequence of events is as follows.
1. The control connection is established from the client port 1176 to the server port
21. (We don't show this.)
2. When the client does the passive open for the data connection on port 1176, it must
specify the SO_REUSEADDR option since that port is already in use by the control
connection on the client.
3. The server does the active open of the data connection (segment 1) from port 20 to
port 1176. The client accepts this (segment 2), even though port 1176 is already in
use on the client, because the two socket pairs file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/ftp_file.htm (13 of 24) [12/09/2001 14.47.49] Chapter 27. FTP: File Transfer Protocol <svr4, 1176, bsdi, 21>
<svr4, 1176, bsdi, 20>
are different (the port numbers on bsdi are different). TCP demultiplexes
incoming segments by looking at the source IP address, source port number,
destination IP address, and destination port number, so as long as one of the four
elements differs, all is OK.
4. The server does the active close of the data connection (segment 5), which puts the
<svr4, 1176, bsdi, 20>
in a 2MSL wait on the server.
5. The client sends another LIST command across the control connection. (We don't
show this.) Before doing this the client does a passive open on port 1176 for its end
of the data connection. The client must specify the SO_REUSEADDR option again,
since the port number 1176 is already in use.
6. The server issues an active open for the data connection from port 20 to port 1176.
Before doing this the server must specify SO_REUSEADDR, since the local port
(20) is associated with a connection that...
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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