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Binh.
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binh 2005-01-17 13:25:33 +00:00
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<sect1 id="PPP-SLIP">
<title>PPP-SLIP</title>
<para>
3.7. PPP, SLIP, PLIP
The Linux kernel has built-in support for PPP (Point-to-Point-
Protocol), SLIP (Serial Line IP) and PLIP (Parallel Line IP). PPP is
the most popular way individual users access their ISPs (Internet
Service Providers). PLIP allows the cheap connection of two machines.
It uses a parallel port and a special cable, achieving speeds of
10kBps to 20kBps.
· Linux PPP HOWTO <http://metalab.unc.edu/mdw/HOWTO/PPP-HOWTO.html>
· PPP/SLIP emulator <http://metalab.unc.edu/mdw/HOWTO/mini/SLIP-PPP-
Emulator.html>
· PLIP information can be found in The Network Administrator Guide
<http://metalab.unc.edu/mdw/LDP/nag/nag.html>
7.5.1. dip
<para>
dip (Dialup IP) is a smart program that is able to set the speed of
the serial device, command your modem to dial the remote end of the
link, automatically log you into the remote server, search for
messages sent to you by the server and extract information for them
such as your IP address and perform the ioctl necessary to switch your
serial port into SLIP mode. dip has a powerful scripting ability and
it is this that you can exploit to automate your logon procedure.
</para>
<para>
You can find it at: metalab.unc.edu.
</para>
<para>
To install it, try the following:
</para>
<para>
<screen>
user% tar xvzf dip337o-uri.tgz
user% cd dip-3.3.7o
user% vi Makefile
root# make install
</screen>
</para>
<para>
The Makefile assumes the existence of a group called uucp, but you
might like to change this to either dip or SLIP depending on your
configuration.
</para>
7.5.2. slattach
<para>
slattach as contrasted with dip is a very simple program, that is very
easy to use, but does not have the sophistication of dip. It does not
have the scripting ability, all it does is configure your serial
device as a SLIP device. It assumes you have all the information you
need and the serial line is established before you invoke it. slattach
is ideal to use where you have a permanent connection to your server,
such as a physical cable, or a leased line.
</para>
7.5.3. When do I use which ?
<para>
You would use dip when your link to the machine that is your SLIP
server is a dialup modem, or some other temporary link. You would use
slattach when you have a leased line, perhaps a cable, between your
machine and the server and there is no special action needed to get
the link working. See section `Permanent Slip connection' for more
information.
</para>
<para>
Configuring SLIP is much like configuring an Ethernet interface (read
section `Configuring an ethernet device' above). However there are a
few key differences.
</para>
<para>
First of all, SLIP links are unlike ethernet networks in that there is
only ever two hosts on the network, one at each end of the link.
Unlike an ethernet that is available for use as soon are you are
cabled, with SLIP, depending on the type of link you have, you may
have to initialize your network connection in some special way.
</para>
<para>
If you are using dip then this would not normally be done at boot
time, but at some time later, when you were ready to use the link. It
is possible to automate this procedure. If you are using slattach then
you will probably want to add a section to your rc.inet1 file. This
will be described soon.
</para>
<para>
There are two major types of SLIP servers: Dynamic IP address servers
and static IP address servers. Almost every SLIP server will prompt
you to login using a username and password when dialing in. dip can
handle logging you in automatically.
</para>
7.5.4. Static SLIP server with a dialup line and DIP.
<para>
A static SLIP server is one in which you have been supplied an IP
address that is exclusively yours. Each time you connect to the
server, you will configure your SLIP port with that address. The
static SLIP server will answer your modem call, possibly prompt you
for a username and password, and then route any datagrams destined for
your address to you via that connection. If you have a static server,
then you may want to put entries for your hostname and IP address
(since you know what it will be) into your /etc/hosts. You should also
configure some other files such as: rc.inet2, host.conf, resolv.conf,
/etc/HOSTNAME and rc.local. Remember that when configuring rc.inet1,
you don't need to add any special commands for your SLIP connection
since it is dip that does all of the hard work for you in configuring
your interface. You will need to give dip the appropriate information
and it will configure the interface for you after commanding the modem
to establish the call and logging you into your SLIP server.
</para>
<para>
If this is how your SLIP server works then you can move to section
`Using Dip' to learn how to configure dip appropriately.
</para>
7.5.5. Dynamic SLIP server with a dialup line and DIP.
<para>
A dynamic SLIP server is one which allocates you an IP address
randomly, from a pool of addresses, each time you logon. This means
that there is no guarantee that you will have any particular address
each time, and that address may well be used by someone else after you
have logged off. The network administrator who configured the SLIP
server will have assigned a pool of address for the SLIP server to
use, when the server receives a new incoming call, it finds the first
unused address, guides the caller through the login process and then
prints a welcome message that contains the IP address it has allocated
and will proceed to use that IP address for the duration of that call.
</para>
<para>
Configuring for this type of server is similar to configuring for a
static server, except that you must add a step where you obtain the IP
address that the server has allocated for you and configure your SLIP
device with that.
</para>
<para>
Again, dip does the hard work and new versions are smart enough to not
only log you in, but to also be able to automatically read the IP
address printed in the welcome message and store it so that you can
have it configure your SLIP device with it.
</para>
<para>
If this is how your SLIP server works then you can move to section
`Using Dip' to learn how to configure dip appropriately.
</para>
7.5.6. Using DIP.
<para>
As explained earlier, dip is a powerful program that can simplify and
automate the process of dialing into the SLIP server, logging you in,
starting the connection and configuring your SLIP devices with the
appropriate ifconfig and route commands.
</para>
<para>
Essentially to use dip you'll write a `dip script', which is basically
a list of commands that dip understands that tell dip how to perform
each of the actions you want it to perform. See sample.dip that comes
supplied with dip to get an idea of how it works. dip is quite a
powerful program, with many options. Instead of going into all of
them here you should look at the man page, README and sample files
that will have come with your version of dip.
</para>
<para>
You may notice that the sample.dip script assumes that you're using a
static SLIP server, so you know what your IP address is beforehand.
For dynamic SLIP servers, the newer versions of dip include a command
you can use to automatically read and configure your SLIP device with
the IP address that the dynamic server allocates for you. The
following sample is a modified version of the sample.dip that came
supplied with dip337j-uri.tgz and is probably a good starting point
for you. You might like to save it as /etc/dipscript and edit it to
suit your configuration:
</para>
<para>
<screen>
#
# sample.dip Dialup IP connection support program.
#
# This file (should show) shows how to use the DIP
# This file should work for Annex type dynamic servers, if you
# use a static address server then use the sample.dip file that
# comes as part of the dip337-uri.tgz package.
#
#
# Version: @(#)sample.dip 1.40 07/20/93
#
# Author: Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
#
main:
# Next, set up the other side's name and address.
# My dialin machine is called 'xs4all.hacktic.nl' (== 193.78.33.42)
get $remote xs4all.hacktic.nl
# Set netmask on sl0 to 255.255.255.0
netmask 255.255.255.0
# Set the desired serial port and speed.
port cua02
speed 38400
# Reset the modem and terminal line.
# This seems to cause trouble for some people!
reset
# Note! "Standard" pre-defined "errlevel" values:
# 0 - OK
# 1 - CONNECT
# 2 - ERROR
#
# You can change those grep'ping for "addchat()" in *.c...
# Prepare for dialing.
send ATQ0V1E1X4\r
wait OK 2
if $errlvl != 0 goto modem_trouble
dial 555-1234567
if $errlvl != 1 goto modem_trouble
# We are connected. Login to the system.
login:
sleep 2
wait ogin: 20
if $errlvl != 0 goto login_trouble
send MYLOGIN\n
wait ord: 20
if $errlvl != 0 goto password_error
send MYPASSWD\n
loggedin:
# We are now logged in.
wait SOMEPROMPT 30
if $errlvl != 0 goto prompt_error
# Command the server into SLIP mode
send SLIP\n
wait SLIP 30
if $errlvl != 0 goto prompt_error
# Get and Set your IP address from the server.
# Here we assume that after commanding the SLIP server into SLIP
# mode that it prints your IP address
get $locip remote 30
if $errlvl != 0 goto prompt_error
# Set up the SLIP operating parameters.
get $mtu 296
# Ensure "route add -net default xs4all.hacktic.nl" will be done
default
# Say hello and fire up!
done:
print CONNECTED $locip ---> $rmtip
mode CSLIP
goto exit
prompt_error:
print TIME-OUT waiting for sliplogin to fire up...
goto error
login_trouble:
print Trouble waiting for the Login: prompt...
goto error
password:error:
print Trouble waiting for the Password: prompt...
goto error
modem_trouble:
print Trouble occurred with the modem...
error:
print CONNECT FAILED to $remote
quit
exit:
exit
</screen>
</para>
<para>
The above example assumes you are calling a dynamic SLIP server, if
you are calling a static SLIP server, then the sample.dip file that
comes with dip337j-uri.tgz should work for you.
</para>
<para>
When dip is given the get $local command it searches the incoming text
from the remote end for a string that looks like an IP address, ie
strings numbers separated by `.' characters. This modification was put
in place specifically for dynamic SLIP servers, so that the process of
reading the IP address granted by the server could be automated.
</para>
<para>
The example above will automatically create a default route via your
SLIP link, if this is not what you want, you might have an ethernet
connection that should be your default route, then remove the default
command from the script. After this script has finished running, if
you do an ifconfig command, you will see that you have a device sl0.
This is your SLIP device. Should you need to, you can modify its
configuration manually, after the dip command has finished, using the
ifconfig and route commands.
</para>
<para>
Please note that dip allows you to select a number of different
protocols to use with the mode command, the most common example is
cSLIP for SLIP with compression. Please note that both ends of the
link must agree, so you should ensure that whatever you select agrees
with what your server is set to.
</para>
<para>
The above example is fairly robust and should cope with most errors.
Please refer to the dip man page for more information. Naturally you
could, for example, code the script to do such things as redial the
server if it doesn't get a connection within a prescribed period of
time, or even try a series of servers if you have access to more than
one.
</para>
7.5.7. Permanent SLIP connection using a leased line and slattach.
<para>
If you have a cable between two machines, or are fortunate enough to
have a leased line, or some other permanent serial connection between
your machine and another, then you don't need to go to all the trouble
of using dip to set up your serial link. slattach is a very simple to
use utility that will allow you just enough functionality to configure
your connection.
</para>
<para>
Since your connection will be a permanent one, you will want to add
some commands to your rc.inet1 file. In essence all you need to do for
a permanent connection is ensure that you configure the serial device
to the correct speed and switch the serial device into SLIP mode.
slattach allows you to do this with one command. Add the following to
your rc.inet1 file:
</para>
<para>
<screen>
#
# Attach a leased line static SLIP connection
#
# configure /dev/cua0 for 19.2kbps and cslip
/sbin/slattach -p cslip -s 19200 /dev/cua0 &
/sbin/ifconfig sl0 IPA.IPA.IPA.IPA pointopoint IPR.IPR.IPR.IPR up
#
# End static SLIP.
</screen>
</para>
<para>
Where:
</para>
<para>
IPA.IPA.IPA.IPA
represents your IP address.
</para>
<para>
IPR.IPR.IPR.IPR
represents the IP address of the remote end.
</para>
<para>
slattach allocates the first unallocated SLIP device to the serial
device specified. slattach starts with sl0. Therefore the first
slattach command attaches SLIP device sl0 to the serial device
specified and sl1 the next time, etc.
</para>
<para>
slattach allows you to configure a number of different protocols with
the -p argument. In your case you will use either SLIP or cSLIP
depending on whether you want to use compression or not. Note: both
ends must agree on whether you want compression or not.
</para>
7.6. SLIP server.
<para>
If you have a machine that is perhaps network connected, that you'd
like other people be able to dial into and provide network services,
then you will need to configure your machine as a server. If you want
to use SLIP as the serial line protocol, then currently you have three
options as to how to configure your Linux machine as a SLIP server. My
preference would be to use the first presented, sliplogin, as it seems
the easiest to configure and understand, but I will present a summary
of each, so you can make your own decision.
</para>
7.6.1. Slip Server using sliplogin .
<para>
sliplogin is a program that you can use in place of the normal login
shell for SLIP users that converts the terminal line into a SLIP line.
It allows you to configure your Linux machine as either a static
address server, users get the same address everytime they call in, or
a dynamic address server, where users get an address allocated for
them which will not necessarily be the same as the last time they
called.
</para>
<para>
The caller will login as per the standard login process, entering
their username and password, but instead of being presented with a
shell after their login, sliplogin is executed which searches its
configuration file (/etc/slip.hosts) for an entry with a login name
that matches that of the caller. If it locates one, it configures the
line as an 8bit clean line, and uses an ioctl call to convert the line
discipline to SLIP. When this process is complete, the last stage of
configuration takes place, where sliplogin invokes a shell script
which configures the SLIP interface with the relevant ip address,
netmask and sets appropriate routing in place. This script is usually
called /etc/slip.login, but in a similar manner to getty, if you have
certain callers that require special initialization, then you can
create configuration scripts called /etc/slip.login.loginname that
will be run instead of the default specifically for them.
</para>
<para>
There are either three or four files that you need to configure to get
sliplogin working for you. I will detail how and where to get the
software and how each is configured in detail. The files are:
</para>
· /etc/passwd, for the dialin user accounts.
· /etc/slip.hosts, to contain the information unique to each dial-in
user.
· /etc/slip.login, which manages the configuration of the routing
that needs to be performed for the user.
· /etc/slip.tty, which is required only if you are configuring your
server for dynamic address allocation and contains a table of
addresses to allocate
· /etc/slip.logout, which contains commands to clean up after the
user has hung up or logged out.
7.6.1.1. Where to get sliplogin
<para>
You may already have the sliplogin package installed as part of your
distribution, if not then sliplogin can be obtained from:
metalab.unc.edu. The tar file contains both source, precompiled
binaries and a man page.
</para>
<para>
To ensure that only authorized users will be able to run sliplogin
program, you should add an entry to your /etc/group file similar to
the following:
</para>
<para>
<screen>
..
slip::13:radio,fred
..
</screen>
</para>
<para>
When you install the sliplogin package, the Makefile will change the
group ownership of the sliplogin program to slip, and this will mean
that only users who belong to that group will be able to execute it.
The example above will allow only users radio and fred to execute
sliplogin.
</para>
<para>
To install the binaries into your /sbin directory and the man page
into section 8, do the following:
</para>
<para>
<screen>
# cd /usr/src
# gzip -dc .../sliplogin-2.1.1.tar.gz | tar xvf -
# cd sliplogin-2.1.1
# <..edit the Makefile if you don't use shadow passwords..>
# make install
</screen>
</para>
<para>
If you want to recompile the binaries before installation, add a make
clean before the make install. If you want to install the binaries
somewhere else, you will need to edit the Makefile install rule.
</para>
<para>
Please read the README files that come with the package for more
information.
</para>
7.6.1.2. Configuring /etc/passwd for Slip hosts.
<para>
Normally you would create some special logins for Slip callers in your
/etc/passwd file. A convention commonly followed is to use the
hostname of the calling host with a capital `S' prefixing it. So, for
example, if the calling host is called radio then you could create a
/etc/passwd entry that looked like:
</para>
<para>
<screen>
Sradio:FvKurok73:1427:1:radio SLIP login:/tmp:/sbin/sliplogin
</screen>
</para>
<para>
It doesn't really matter what the account is called, so long as it is
meaningful to you.
</para>
<para>
Note: the caller doesn't need any special home directory, as they will
not be presented with a shell from this machine, so /tmp is a good
choice. Also note that sliplogin is used in place of the normal login
shell.
</para>
7.6.1.3. Configuring /etc/slip.hosts
<para>
The /etc/slip.hosts file is the file that sliplogin searches for
entries matching the login name to obtain configuration details for
this caller. It is this file where you specify the ip address and
netmask that will be assigned to the caller and configured for their
use. Sample entries for two hosts, one a static configuration for host
radio and another, a dynamic configuration for user host albert might
look like:
</para>
<para>
<screen>
#
Sradio 44.136.8.99 44.136.8.100 255.255.255.0 normal -1
Salbert 44.136.8.99 DYNAMIC 255.255.255.0 compressed 60
#
</screen>
</para>
<para>
The /etc/slip.hosts file entries are:
</para>
1. the login name of the caller.
2. ip address of the server machine, ie this machine.
3. ip address that the caller will be assigned. If this field is coded
DYNAMIC then an ip address will be allocated based on the
information contained in your /etc/slip.tty file discussed later.
Note: you must be using at least version 1.3 of sliplogin for this
to work.
4. the netmask assigned to the calling machine in dotted decimal
notation eg 255.255.255.0 for a Class C network mask.
5. the slip mode setting which allows you to enable/disable
compression and slip other features. Allowable values here are
"normal" or "compressed".
6. a timeout parameter which specifies how long the line can remain
idle (no datagrams received) before the line is automatically
disconnected. A negative value disables this feature.
7. optional arguments.
<para>
Note: You can use either hostnames or IP addresses in dotted decimal
notation for fields 2 and 3. If you use hostnames then those hosts
must be resolvable, that is, your machine must be able to locate an ip
address for those hostnames, otherwise the script will fail when it is
called. You can test this by trying trying to telnet to the hostname,
if you get the `Trying nnn.nnn.nnn...' message then your machine has
been able to find an ip address for that name. If you get the message
`Unknown host', then it has not. If not, either use ip addresses in
dotted decimal notation, or fix up your name resolver configuration
(See section Name Resolution).
</para>
<para>
The most common slip modes are:
</para>
<para>
normal
to enable normal uncompressed SLIP.
</para>
<para>
compressed
to enable van Jacobsen header compression (cSLIP)
</para>
<para>
Naturally these are mutually exclusive, you can use one or the other.
For more information on the other options available, refer to the man
pages.
</para>
7.6.1.4. Configuring the /etc/slip.login file.
<para>
After sliplogin has searched the /etc/slip.hosts and found a matching
entry, it will attempt to execute the /etc/slip.login file to actually
configure the SLIP interface with its ip address and netmask.
</para>
<para>
The sample /etc/slip.login file supplied with the sliplogin package
looks like this:
</para>
<para>
<screen>
#!/bin/sh -
#
# @(#)slip.login 5.1 (Berkeley) 7/1/90
#
# generic login file for a SLIP line. sliplogin invokes this with
# the parameters:
# $1 $2 $3 $4, $5, $6 ...
# SLIPunit ttyspeed pid the arguments from the slip.host entry
#
/sbin/ifconfig $1 $5 pointopoint $6 mtu 1500 -trailers up
/sbin/route add $6
arp -s $6 <hw_addr> pub
exit 0
#
</screen>
</para>
<para>
You will note that this script simply uses the ifconfig and route com­
mands to configure the SLIP device with its ipaddress, remote ip
address and netmask and creates a route for the remote address via the
SLIP device. Just the same as you would if you were using the slattach
command.
</para>
<para>
Note also the use of Proxy ARP to ensure that other hosts on the same
ethernet as the server machine will know how to reach the dial-in
host. The <hw_addr> field should be the hardware address of the
ethernet card in the machine. If your server machine isn't on an
ethernet network then you can leave this line out completely.
</para>
7.6.1.5. Configuring the /etc/slip.logout file.
<para>
When the call drops out, you want to ensure that the serial device is
restored to its normal state so that future callers will be able to
login correctly. This is achieved with the use of the
/etc/slip.logout file. It is quite simple in format and is called with
the same argument as the /etc/slip.login file.
</para>
<para>
<screen>
#!/bin/sh -
#
# slip.logout
#
/sbin/ifconfig $1 down
arp -d $6
exit 0
#
</screen>
</para>
<para>
All it does is `down' the interface which will delete the manual route
previously created. It also uses the arp command to delete any proxy
arp put in place, again, you don't need the arp command in the script
if your server machine does not have an ethernet port.
7.6.1.6. Configuring the /etc/slip.tty file.
</para>
<para>
If you are using dynamic ip address allocation (have any hosts
configured with the DYNAMIC keyword in the /etc/slip.hosts file, then
you must configure the /etc/slip.tty file to list what addresses are
assigned to what port. You only need this file if you wish your server
to dynamically allocate addresses to users.
</para>
<para>
The file is a table that lists the tty devices that will support dial-
in SLIP connections and the ip address that should be assigned to
users who call in on that port.
</para>
<para>
Its format is as follows:
</para>
<para>
<screen>
# slip.tty tty -> IP address mappings for dynamic SLIP
# format: /dev/tty?? xxx.xxx.xxx.xxx
#
/dev/ttyS0 192.168.0.100
/dev/ttyS1 192.168.0.101
#
</screen>
</para>
<para>
What this table says is that callers that dial in on port /dev/ttyS0
who have their remote address field in the /etc/slip.hosts file set to
DYNAMIC will be assigned an address of 192.168.0.100.
</para>
<para>
In this way you need only allocate one address per port for all users
who do not require an dedicated address for themselves. This helps you
keep the number of addresses you need down to a minimum to avoid
wastage.
</para>
7.6.2. Slip Server using dip .
<para>
Let me start by saying that some of the information below came from
the dip man pages, where how to run Linux as a SLIP server is briefly
documented. Please also beware that the following has been based on
the dip337o-uri.tgz package and probably will not apply to other
versions of dip.
</para>
<para>
dip has an input mode of operation, where it automatically locates an
entry for the user who invoked it and configures the serial line as a
SLIP link according to information it finds in the /etc/diphosts file.
This input mode of operation is activated by invoking dip as diplogin.
This therefore is how you use dip as a SLIP server, by creating
special accounts where diplogin is used as the login shell.
</para>
<para>
The first thing you will need to do is to make a symbolic link as
follows:
</para>
<para>
<screen>
# ln -sf /usr/sbin/dip /usr/sbin/diplogin
</screen>
</para>
<para>
You then need to add entries to both your /etc/passwd and your
/etc/diphosts files. The entries you need to make are formatted as
follows:
</para>
<para>
To configure Linux as a SLIP server with dip, you need to create some
special SLIP accounts for users, where dip (in input mode) is used as
the login shell. A suggested convention is that of having all SLIP
accounts begin with a capital `S', eg `Sfredm'.
</para>
<para>
A sample /etc/passwd entry for a SLIP user looks like:
</para>
<para>
<screen>
Sfredm:ij/SMxiTlGVCo:1004:10:Fred:/tmp:/usr/sbin/diplogin
^^ ^^ ^^ ^^ ^^ ^^ ^^
| | | | | | \__ diplogin as login shell
| | | | | \_______ Home directory
| | | | \____________ User Full Name
| | | \_________________ User Group ID
| | \_____________________ User ID
| \_______________________________ Encrypted User Password
\__________________________________________ Slip User Login Name
</screen>
</para>
<para>
After the user logs in, the login program, if it finds and verifies
the user ok, will execute the diplogin command. dip, when invoked as
diplogin knows that it should automatically assume that it is being
used a login shell. When it is started as diplogin the first thing it
does is use the getuid() function call to get the userid of whoever
has invoked it. It then searches the /etc/diphosts file for the first
entry that matches either the userid or the name of the tty device
that the call has come in on and configures itself appropriately. By
judicious decision as to whether to give a user an entry in the
diphosts file, or whether to let the user be given the default
configuration you can build your server in such a way that you can
have a mix of static and dynamically assigned address users.
</para>
<para>
dip will automatically add a `Proxy-ARP' entry if invoked in input
mode, so you do not need to worry about manually adding such entries.
</para>
7.6.2.1. Configuring /etc/diphosts
<para>
/etc/diphosts is used by dip to lookup preset configurations for
remote hosts. These remote hosts might be users dialing into your
linux machine, or they might be for machines that you dial into with
your linux machine.
</para>
<para>
The general format for /etc/diphosts is as follows:
</para>
<para>
<screen>
..
Suwalt::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:CSLIP,1006
ttyS1::145.71.34.3:145.71.34.2:255.255.255.0:Dynamic ttyS1:CSLIP,296
..
</screen>
</para>
<para>
The fields are:
</para>
1. login name: as returned by getpwuid(getuid()) or tty name.
2. unused: compat. with passwd
3. Remote Address: IP address of the calling host, either numeric or
by name
4. Local Address: IP address of this machine, again numeric or by name
5. Netmask: in dotted decimal notation
6. Comment field: put whatever you want here.
7. protocol: Slip, CSlip etc.
8. MTU: decimal number
<para>
An example /etc/net/diphosts entry for a remote SLIP user might be:
</para>
<para>
<screen>
Sfredm::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:SLIP,296
</screen>
</para>
<para>
which specifies a SLIP link with remote address of 145.71.34.1 and MTU
of 296, or:
</para>
<para>
<screen>
Sfredm::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:CSLIP,1006
</screen>
</para>
<para>
which specifies a cSLIP-capable link with remote address 145.71.34.1
and MTU of 1006.
</para>
<para>
Therefore, all users who you wish to be allowed a statically allocated
dial-up IP access should have an entry in the /etc/diphosts. If you
want users who call a particular port to have their details
dynamically allocated then you must have an entry for the tty device
and do not configure a user based entry. You should remember to
configure at least one entry for each tty device that your dialup
users use to ensure that a suitable configuration is available for
them regardless of which modem they call in on.
</para>
<para>
When a user logs in they will receive a normal login and password
prompt at which they should enter their SLIP-login userid and
password. If these verify ok then the user will see no special
messages and they should just change into SLIP mode at their end. The
user should then be able to connect ok and be configured with the
relevant parameters from the diphosts file.
</para>
7.6.3. SLIP server using the dSLIP package.
<para>
Matt Dillon <dillon@apollo.west.oic.com> has written a package that
does not only dial-in but also dial-out SLIP. Matt's package is a
combination of small programs and scripts that manage your connections
for you. You will need to have tcsh installed as at least one of the
scripts requires it. Matt supplies a binary copy of the expect utility
as it too is needed by one of the scripts. You will most likely need
some experience with expect to get this package working to your
liking, but don't let that put you off.
</para>
<para>
Matt has written a good set of installation instructions in the README
file, so I won't bother repeating them.
</para>
<para>
You can get the dSLIP package from its home site at:
</para>
<para>
apollo.west.oic.com
/pub/linux/dillon_src/dSLIP203.tgz
</para>
<para>
or from:
</para>
<para>
metalab.unc.edu
/pub/Linux/system/Network/serial/dSLIP203.tgz
</para>
<para>
Read the README file and create the /etc/passwd and /etc/group entries
before doing a make install.
</para>
</sect1>

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