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From: Joe Greco <jgreco@brasil.moneng.mei.com>
Message-Id: <199511210814.CAA05743@brasil.moneng.mei.com>
Subject: Re: Pseudo SLIP
To: joerg_wunsch@uriah.heep.sax.de
Date: Tue, 21 Nov 1995 02:14:49 -0600 (CST)
Cc: radova@risc6.unisa.ac.za, hackers@FreeBSD.ORG
In-Reply-To: <199511210034.BAA14607@uriah.heep.sax.de> from "J Wunsch" at Nov 21, 95 01:34:02 am
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> As A. Radovanovic wrote:
> > 
> > I am looking for a public domain pseudo slip package I want to run
> > on the 2.0. Could anybody recommend me one?
> 
> What's ``pseudo SLIP''?

It means: "pretends to be real SLIP."

There are two mainstream SLIP/PPP emulators that I am aware of:  tia and
slirp.  slirp is free, tia isn't.  slirp is based on FreeBSD 2.0R networking
code.  :-)

For those who are interested in how it works, a user compiles slirp in a
standard shell account, and runs it.  slirp starts a pseudo-TCP/IP session.
slirp accepts TCP/IP packets from the user and evaluates them, and may use
the host system's standard C library network calls
(socket/bind/connect/et.al) to "proxy" for the client.  The end result:  you
"telnet" to an address from your PC at home, slirp interprets the connection
request, and opens a TCP socket from the host system to the requested
destination.  It then passes data back and forth, encapsulating it within
reasonable SLIP packets on your PC's side, using standard user-level system
calls on the host side.  It spoofs having a real SLIP connection.

Quite a nifty little concept.  It has a number of (dis)advantages.  Since
the host system is acting as a "proxy", no additional IP addresses are
required.  All requests appear to real Internet systems as though they come
from the host system - because they do.  The slirp client sees a standard
SLIP connection (which can't do certain things, mostly those things that
would require an Internet host to initiate a connection to an arbitrary port
on the slirp client).

... JG