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SLIP/PPP Emulator mini-HOWTO


Glen Reesor - Converted document from HTML to DocBook v4.1 (SGML)

Revision History                                                             
Revision 3.1       21 February 2001             Revised by: GCR              
Revision 3.0       7 August 1997                Revised by: Irish            

This document will describe how to get your Linux box to connect to a generic
site via a SLIP/PPP emulator, such as SLiRP or TIA. I take no responsibility
for your use of this information, but corrections are welcome.

I will not attempt to describe all that can be done over this connection once
established, but I will refer you to other documents or sites that will
contain the relevant information.

That done, let's do it!

Table of Contents
1. Introduction
    1.1. Copyright Information
    1.2. Disclaimer
    1.3. New Versions
    1.4. Feedback
2. How Does an Emulator Work?
    2.1. What is TIA?
    2.2. What is SLiRP?
    2.3. What about Term?
    2.4. What about real SLIP/PPP?
3. Prerequisites
4. Preparing your Linux Machine
    4.1. Compiling your Kernel
    4.2. Edit some files in /etc
    4.3. DIP
    4.4. PPP
5. Now What?
    5.1. Mail
    5.2. News
    5.3. Mosaic/Netscape
6. Miscellaneous
    6.1. References

1. Introduction

I am Irish, <>, available for comment on Linux almost
everyday, when I'm not petting my cat or hugging my kid.

This HOWTO is available in the following places:

��*�[] ftp://

1.1. Copyright Information

This document is copyrighted (c) 2001 Irish and is distributed under the
terms of the Linux Documentation Project (LDP) license, stated below.

Unless otherwise stated, Linux HOWTO documents are copyrighted by their
respective authors. Linux HOWTO documents may be reproduced and distributed
in whole or in part, in any medium physical or electronic, as long as this
copyright notice is retained on all copies. Commercial redistribution is
allowed and encouraged; however, the author would like to be notified of any
such distributions.

All translations, derivative works, or aggregate works incorporating any
Linux HOWTO documents must be covered under this copyright notice. That is,
you may not produce a derivative work from a HOWTO and impose additional
restrictions on its distribution. Exceptions to these rules may be granted
under certain conditions; please contact the Linux HOWTO coordinator at the
address given below.

In short, we wish to promote dissemination of this information through as
many channels as possible. However, we do wish to retain copyright on the
HOWTO documents, and would like to be notified of any plans to redistribute
the HOWTOs.

If you have any questions, please contact <>

1.2. Disclaimer

No liability for the contents of this documents can be accepted. Use the
concepts, examples and other content at your own risk. As this is a new
edition of this document, there may be errors and inaccuracies, that may of
course be damaging to your system. Proceed with caution, and although this is
highly unlikely, the author(s) do not take any responsibility for that.

All copyrights are held by their by their respective owners, unless
specifically noted otherwise. Use of a term in this document should not be
regarded as affecting the validity of any trademark or service mark.

Naming of particular products or brands should not be seen as endorsements.

You are strongly recommended to take a backup of your system before major
installation and backups at regular intervals.

1.3. New Versions

The latest version number of this document can be found at:

��*�[] ftp://

1.4. Feedback

Feedback is most certainly welcome for this document. Without your
submissions and input, this document wouldn't exist. Please send your
additions, comments and criticisms to the following email address : <>.

2. How Does an Emulator Work?

It is important to understand how a SLIP/PPP emulator works in general, to be
aware of its limitations. First, you do not need to install the emulator on
your machine. It runs on your remote host only. What you need on your machine
is the TCP/IP and SLIP or PPP protocols installed in your kernel (more on
that in a bit), and some clients.

Here's what happens: you send network requests from your machine to your
remote host over the SLIP/PPP link. The emulator grabs them and sends them
out to the Net at large. Then, incoming data is sent back from the Net to
your account on the remote host, where the emulator grabs it and sends it
back over the SLIP/PPP link to your machine. So, to the Net it appears as if
you are working out of your account on the remote host, but to you it looks
like you are really connected right to the Net.

As you can see, this can confuse stuff that is incoming from the Net. For
example, talk doesn't work via an emulator, because the incoming talk request
tries to start the remote hosts talk daemon, not yours.

The other big difference between an emulator and real SLIP/PPP is you are NOT
assigned your own IP address; remember, you are only converting a dialup
account to a SLIP/PPP connection.

2.1. What is TIA?

[] The Intenet Adaptor was written
by the fine folks at They have quit working on it now, and
consider it a 'mature' product. The last version is 2.05; if you are going to
use TIA, please get this version.

    Note: At last report, have gone out of business.
2.2. What is SLiRP?

This is a freeware application, covered under the GNU Public License. It is
out of beta, and is real stable. It sports a few more features than TIA, and
is (reportedly) easier on host resources. Available at fine Linux FTP sites

2.3. What about Term?

If you don't have root access to your machine for one reason or another, and
you can't persuade someone who does to install SLIP and dip, then you won't
have much choice except to use Term. If you want to know more about Term,
please read the HOWTO on Sunsite.

2.4. What about real SLIP/PPP?

Hey, a lot of places are offering real SLIP/PPP at reasonable prices for
non-dedicated dialup nowadays. If you can afford it, or feel the need, go for
it. The Real Thing is always better than emulation. However, one of the
things an emulator provides is security; it acts as an impregnable firewall,
and with it you are pretty much as bulletproof as your provider is. You'll
pay for it though, emulation is slower, and does not fully support every
protocol. Still and all, emulation is good enough for most people, and is a
fine way to connect to the Net.

3. Prerequisites

Enough already! How do I set it up?

Alright hotrod, we're getting there, but first there's some info you need to
get, and a couple of explanations.

First, you need to get the IP address of your provider, if you don't have it
already. You can do this by typing 'who' at a shell prompt there, or reading
their /etc/hosts, or even just asking them. While your getting that, get the
IP address of the POP/SMTP host and the NNTP server (if you don't know what
those are, trust me and ask for them anyway, you'll need 'em).

Next, let me explain quickly about hostnames and domain names. The hostname
is the first part of a machines name, the domain is the rest of it. Like
this: (a four parter would be
Together, they make a Fully Qualified Domain Name (FQDN).

The name of your Linux machine is stored in /etc/HOSTNAME, and yes, you can
change it. In fact, please do (if you're using Slackware, it'll be
"" by default). Just edit the /etc/HOSTNAME file to be
whatever you want - remember, if you are using an emulator, you are
essentially invisible to the Net at large, so you can be creative. However,
if you plan to get a real SLIP/PPP connection down the road sometime, you'll
probably want to conform to being a sub-host of your provider. For example,
if your provider is "", the domain is "" and
the hostname is "info". So you could either be ""
or just "". Either would work, and in either case your
hostname is "offramp".

4. Preparing your Linux Machine

In a nutshell, here's what's required. I'll explain the first three in

��*�Compile your kernel to include SLIP and TCP/IP
��*�Edit some files in /etc
��*�Install and configure dip
��*�Install pppd (optional, for PPP only)

You will also need to get an emulator binary appropriate for your remote host
and install it. SLiRP is available at [
index.html] Sunsite and other fine Linux FTP sites. All of the relevant info
for TIA is available at [] TIAs home

That's it! Let's get started.

4.1. Compiling your Kernel

If you have never done this, you should. And you should read the FAQ first,
but don't worry, it's easy. If you want, you can e-mail me and I'll help.

I'll assume that you have here, for the sake of brevity. When you 'make
config', look for "Network Devices". Say 'y', of course, then say 'y' to
SLIP, CSLIP, (or PPP) and TCP/IP and 'n' to everything else, unless you have
ethercards or need some other protocol for something else. If you don't do
this, it won't work! Finish compiling and installing the new kernel, then,

4.2. Edit some files in /etc

These files will set up your routes to your remote host. /etc is the
directory for system configurations. Replace everything in double quotes with
the appropriate values, naturally (but don't include the quotes - they are
there for reference). There are three files you need to edit, they are:

    #The next line is required to be EXACTLY as below.                      localhost                                             
    #Note at the end of the next two entries the hostname is repeated.    
    #This abbreviation is an alias, and is required for the first entry.  
    #If you're on a LAN, you'll need to substitute your IP address for    
    #the first one below.                                                   "  yourhostname"              
    "XXX.XXX.XX.XX" "  remotehostname"          
    order hosts, bind                                                
    multi on                                                         
    domain ""                                                    
    #The next line usually uses the same remote IP address that's in /etc/hosts 
    nameserver "XXX.XXX.XX.XX"                                                  
��*�To use an NNTPserver, put this line in your /etc/profile
    export NNTPSERVER="remote.hosts.nntpservername"                  

4.3. DIP

DIP (Dialup Internet Protocol) is what you will use to dial up the remote
host, start the emulator, and convert the line to SLIP/PPP. It comes in the
"N" set of Slackware, along with a bunch of clients and utilities, some of
which you may want to install also =). It is also available at [ftp://] Sunsite in an individual tar file

Once you have it installed, you will need to have a dip script, Here's a
sample, just plug in the appropriate stuff where the double quotes are (but
don't include the quotes, they are there for reference).
  get $local ""                                      
  get $remote ""                                   
#Your port here                                                              
  port cua"?"                                                                
#Use 115200 for 28.8 modems                                                  
  speed 57400                                                                
#don't use spaces in your AT command string!                                 
  init AT "string of commands"                                               
  wait OK 5                                                                  
# This will redial. If it doesn't work, play with the wait time (listen      
# to your modem). If it still doesn't work, mail me.                         
# See also; the note at the bottom of the script re: error codes.            
  dial "phonenumber"                                                         
  print Dialing...                                                           
  if $errlvl != 0 goto error                                                 
#You may need to change this wait time to suit your modem                    
  wait BUSY 20                                                               
  if $errlvl == 0 goto dial                                                  
  print Connected and Logging in...                                          
#This wait and send gets me past my hosts Annex. Change for your site!       
  wait ==> 60                                                                
  send 4\n                                                                   
  wait ogin: 60                                                              
  if $errlvl != 0 goto login_error1                                          
  send "LOGIN"\n                                                             
  wait assword: 60                                                           
  if $errlvl != 0 goto login_error2                                          
  send "PASSWORD"\n                                                          
  wait "SYSTEM PROMPT" 60                                                    
  if $errlvl != 0 goto shell_error                                           
  print Logged in!                                                           
  send "emulator startup command"\n                                          
  wait "emulator startup response" 60                                        
  if $errlvl != 0 goto emu_error                                             
#The recommended mtu setting is 1500, but this is faster interactively.      
#Ftp may be slower, so adjust to taste.                                      
  get $mtu 296                                                               
  print CONNECTED to $remote with address $rmtip                             
  mode CSLIP                                                                 
  goto exit                                                                  
  print Dialing Error                                                        
  print No Login                                                             
  print No Password prompt                                                   
  print No shell prompt                                                      
  There was a problem starting the emulator                                  
#This will error out when the -v flag is used, but work when run normally    
#(ends dip at a local prompt).                                               

4.3.1. DIP Notes

Newer versions of dip don't return modem status codes (BUSY, NO CONNECT,
etc.), they use numbers instead. Here's a table:

��*�0 = OK
��*�1 = CONNECT
��*�2 = ERROR
��*�3 = BUSY
��*�4 = NO CARRIER

This would make your dial section look like this:
  dial "phonenumber"                                                         
  print Dialing...                                                           
  if $errlvl != 0 goto error                                                 
  wait 1 20                                                                  
  if $errlvl != 1 goto dial                                                  

Thanks to Lee Olds <> for that bit.

\n = newline, \r = carriage return. You may require one or the other (or
both) in the appropriate places. If the ones provided don't work, experiment.

A word about the form of the wait and sends. If it isn't clear by the
example, here's what's happening:

wait ogin: 60
    The script will wait for the remote to send 'ogin:' for 60 seconds. When
    it gets it, the script advances. If it doesn't get it, it will advance
    after the timeout of 60 seconds.
if $errlvl != 0 goto login_error
    (This whole line is optional.) If the script is advancing because it got
    what it was waiting for, this gets skipped. if the script is advancing
    because it timed out, it will go to where you tell it to ('login_error1'
    in this case.
send "LOGIN"\n
    DIP will send 'LOGIN' and a newline

You can put in sleep statements if you need to, like this: "sleep 10" This
will make the script pause for 10 seconds.

After editing this file, rename it, say, remote.dip and put it in /root.
Then, as root, run 'dip remote'. Use the -v flag the first time to debug it
('dip -v remote'), this will show you all the steps dip takes.

Dip will only run as root, but there is a way to make it run from a user
account. For now, if you need this info, ask. I may include it in this file
later if enough people want it.

If dip errors out right away, try removing the comments from the script.

4.4. PPP

The above gets you rolling with CSLIP, which is really fine most of the time.
It truly is easy to get working, since the protocol is supported at the
kernel level - just make sure it's in there and it works.

However, some of you will want PPP, for what reasons, only you can say. I'm
not going to tell you how to set it up here, there's a whole other HOWTO
written just for that. What I will do is tell you what the gotchas are when
using PPP with an emulator.

First, the latest version of DIP says you can use it to start PPP, and you
can, BUT it only starts the PPP daemon - no flags, nothing. So if you want to
use DIP to start PPP, be sure to put all of your startup info in the /etc/ppp
/options file, or it won't work.

Speaking of the options file, one of the things that MUST be in there no
matter how you start pppd is this: ''. What this is is
'localIPaddress:remoteIPaddress'. You need it there because normally pppd can
fill in the blank itself, but fails when connecting to an emulator.

Be sure to get the latest and greatest pppd package. It seems there were a
few versions recently that had a bit of trouble.

Lastly, unless you have a good reason to use PPP, or just want to learn how
it works, you really don't need it. I have tried them both, and didn't notice
any performance difference with the standard set of clients. Of course, Your
Mileage May Vary. :)

5. Now What?

Hey, if all went well, you are now connected to the Net! Try a 'telnet
remotehostname' (remember that abbreviation in your hosts file?). You should
get the remotes telnet login prompt. Go on, try it! You can now telnet/FTP/
etc. anywhere on the Net from your local machine. How? Your machine is using
the remote as a nameserver to resolve addresses (resolv.conf). Experiment,
find out what works and what doesn't.

You will not be able to use services that are not provided already on your
remote host! For example, if your server doesn't allow telnets, chances are
you can't do it either. Why? Because the emulator is only re-directing what
is already available.

5.1. Mail

The obvious text based solution is Pine, you can get it from [ftp://] The University of Washington .

My pick for 'Best Mail Reader, X Based' has to go to XFmail. This has now
gotten out of beta, and rocks. Easy to install; requires no local mail system
be installed (but will work with local spools) because it has POP built in -
no more popclient/fetchpop! Easy to use; totally customizable from the GUI.
Also supports MIME. Get it from [
xfmail.html] The XFmail Homesite.

5.2. News

The text based News Reader [] SLRN is
fairly simple to install and use. It is a true NNTP newsreader, which means 
no local news transport is required to make it work (you don't have install
Cnews or INN). It does require that you have access to an NNTPserver,
naturally, but most ISPs have this. It is text based, but has color and mouse
support, and runs fine in an rxvt window.

The X based News Reader [] KNews is almost
perfect. As with SLRN above, no local transport is required, but an NNTP
server is. It's at least worth a look.

5.3. Mosaic/Netscape

Obviously, you will need to have X running for this to work, but it's a
simple matter of FTPing the binary, unpacking it, and installing it.

6. Miscellaneous

If I've left anything out, or you still have questions, I read my mail daily.
This information gets updated fairly regularly, so keep checking back every
so often (I'll change the version numbers). Naturally, the more you
contribute, the more info will be included here, so don't hesitate to tell me
about whatever you have to offer.

If you would like some help, or are having trouble with your setup, I'll help
but you must send me the following info:

 1. A copy of your three /etc files.
 2. A copy of your script output, run with the -v flag (please remove your
    password from this!)

Even if you don't have anything to contribute, but used this info
sucsessfully, please mail me. I want to know how useful this really is.

6.1. References

Sunsite is the FTP site [], a veritable plethora of everything Linux, including almost
every FAQ, HOWTO, and README written.

[] is the home of TIA, the only place
it is available.

    Note: appears to be out of business.
I am Irish, <>, available for comment on Linux almost
everyday, when I'm not petting my cat or hugging my kid.

This HOWTO is available in the following places:

��*�[] ftp://

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