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Rlogin uses a single TCP connection between the client and server. After the normal TCP
connection establishment is complete, the following application protocol takes place
between the client and server.
1. The client writes four strings to the server; (a) a byte of 0, (b) the login name of the
user on the client host, terminated by a byte of 0, (c) the login name of the user on
the server host, terminated by a byte of 0, (d) the name of the user's terminal type,
followed by a slash, followed by the terminal speed, terminated by a byte of 0. Two
login names are required because users aren't required to have the same login name
on each system.
The terminal type is passed from the client to the server because many full-screen
applications need to know it. The terminal speed is passed because some
applications operate differently depending on the speed. For example, the vi editor
works with a smaller window when operating at slower speeds, so it doesn't take
forever to redraw the window.
2. The server responds with a byte of 0.
3. The server has the option of asking the user to enter a password. This is handled as
normal data exchange across the Rlogin connection-there is no special protocol. The
server sends a string to the client (which the client displays on the terminal), often
Password:. If the client does not enter a password within some time limit (often
60 seconds), the server closes the connection. file:///D|/Documents%20and%20Settings/bigini/Documenti/homenet2run/tcpip/tcp-ip-illustrated/telnet.htm (3 of 26) [12/09/2001 14.47.45] Chapter 26. Telnet and Rlogin: Remote Login We can create a file in our home directory on the server (named .rhosts) with
lines containing a hostname and our username. If we login from the specified host
with that username, we are not prompted for a password. Most security texts, such
as [Curry 1992], strongly suggest never using this feature because of the security
hole it presents.
If we are prompted by the server for a pas...
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