04-30-2005
This is a TCP concept. TCP guarantees reliable dilevery of data. It does this by using sequence numbers. Each byte of data gets a sequence number. Both sides of the connection keep the other side informed of the sequence number of the next byte of data it needs to recieve. The sequence numbers do not start at 0 or 1. The initial sequence number is random. So both sides need to syncronize ISN's. This establishes a TCP connection.
1. The client sends a packet with it's ISN. This packet has a SYN flag. This packet is addressed to some well-known port on the server. And it has the local port number the client has picked for itself.
2. The server send a packet back to client. This packet does two things. First it sets the ACK flag and and sets the ack number to the client's ISN+1. And it sets the SYN flag and sends it's own ISN.
3. The client sends a packet to ACK the server's ISN+1.
At this point both client and server know each other's sequence numbers.
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LEARN ABOUT ULTRIX
rlogind
rlogind(8c) rlogind(8c)
Name
rlogind - remote login server
Syntax
/etc/rlogind
Description
The server is used for the program. The server provides a remote login facility with authentication based on privileged port numbers.
The server is invoked by when it receives a connection on the port indicated in the login service specification. For further information,
see When a service request is received, the following protocol is initiated:
1. The server checks the client's source port. If the port is not in the range 0-1023, the server aborts the connection.
2. The server checks the client's source address and requests the corresponding host name. If the hostname cannot be determined, the dot-
notation representation of the host address is used.
Once the source port and address have been checked, allocates a pseudo terminal and manipulates file descriptors so that the slave half of
the pseudo terminal becomes the stdin, stdout, and stderr for a login process. For further information, see
The login process is an instance of the program, invoked with the option. The login process then proceeds with the authentication process
as described in but if automatic authentication fails, it reprompts the user to log in on a standard terminal line.
The parent of the login process manipulates the master side of the pseudo terminal, operating as an intermediary between the login process
and the client instance of the program. In normal operation, the packet protocol described in is invoked to provide ^S/^Q type facilities
and propagate interrupt signals to the remote programs. The login process propagates the client terminal's baud rate and terminal type, as
found in the environment variable, TERM. For further information see
The screen or window size of the terminal is requested from the client, and any changes in the window size from the client are sent to the
pseudo terminal.
Restrictions
The authentication procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but it is
useful in an open environment.
Diagnostics
All diagnostic messages are returned on the connection associated with the stderr, after which any network connections are closed. An
error is indicated by a leading byte with a value of 1.
Hostname for your address unknown
No entry in the host name database existed for the client's machine.
Try again
A fork by the server failed.
/bin/sh: ...
The user's login shell could not be started.
See Also
rlogin(1c), inetd(8c)
rlogind(8c)