TCP/IP and the server<->client model

[jbn at wdl1.UUCP]

The basic concept of a connection in the IP/TCP world is that ALL of
the following information is used to uniquely identify a connection.

	Source Internet Address			(32 bits)
	Source TCP Port				(16 bits)
	Destination Internet Address		(32 bits)
	Destination TCP Port			(16 bits)

Servers normally perform a passive TCP open specifying the Destination
Internet Address and Destination TCP port, but leaving the rest unspecified.
Users then perform TCP opens specifying all four parameters.  When the
first datagram (the TCP SYN packet) arrives at the destination, the matching 
passive open is ``bound'' to the full connection specification, and thereafter
that open talks only to the other end to which it is now bound.

The easiest way to build a server daemon of your own under 4.2BSD is to start 
with one of the simple ones (``rexecd'' is a good choice) and go from there.

						John Nagle