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Unformatted text preview: sword, what we type is sent to the server
as cleartext. Each character of the password that we type is sent as is. Anyone who
can read the raw network packets can read the characters of our password. Newer
implementations of the Rlogin client, such as 4.4BSD, first try to use Kerberos,
which avoids sending cleartext passwords across the network. This requires a
compatible server that also supports Kerberos. ([Curry 1992] describes Kerberos in
4. The server normally sends a request to the client asking for the terminal's window
size (described later).
The client sends 1 byte at a time to the server and all echoing is done by the server. We saw
this in Section 19.2. Also, the Nagle algorithm is normally enabled (Section 19.4), causing
multiple input bytes to be sent as a single TCP segment across slower networks. The
operation is simple: everything typed by the user is sent to the server, and everything sent
by the server to the client is displayed on the terminal.
Additional commands exist that can be sent from the client to the server and from the
server to the client. Let's first describe the scenarios that require these commands.
By default, flow control is done by the Rlogin client. The client recognizes the ASCII
STOP and START characters (Control-S and Control-Q) typed by the user, and stops or
starts the terminal output.
If this isn't done, each time we type Control-S to stop the terminal output, the Control-S
character is sent across the network to the server, and the server stops writing to the
network-but up to a window's worth of output may have been already written by the server
and will be displayed before the output is stopped. Hundreds or thousands of bytes of data
will scroll down the screen before the output stops. Figure 26.3 shows this scenario. Figure 26.3 Rlogin connection if server performs STOP/START processing.
To an interactive user this delayed response to the Control-S character is bad. file:///D|/Documents%20and%20Sett...
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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