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## 5.3.3 SLIP Configuration

SLIP (Serial Line Internet Protocol) allows you to use TCP/IP over a serial line, be that a phone line, with a dialup modem, or a leased asynchronous line of some sort. Of course, to use SLIP you'll need access to a dial-in SLIP server in your area. Many universities and businesses provide SLIP access for a modest fee.

There are two major SLIP-related programs available---`dip` and `slattach`. Both of these programs are used to initiate a SLIP connection over a serial device. It is necessary to use one of these programs in order to enable SLIP---it will not suffice to dial up the SLIP server (with a communications program such as `kermit`) and issue `ifconfig` and `route` commands. This is because `dip` and `slattach` issue a special ioctl() system call to seize control of the serial device to be used as a SLIP interface.

`dip` can be used to dial up a SLIP server, do some handshaking to login to the server (exchanging your username and password, for example) and then initate the SLIP connection over the open serial line. `slattach`, on the other hand, does very little other than grab the serial device for use by SLIP. It is useful if you have a permanent line to your SLIP server and no modem dialup or handshaking is necessary to initiate the connection. Most dialup SLIP users should use `dip`, on the other hand.

`dip` can also be used to configure your Linux system as a SLIP server, where other machines can dial into your own and connect to the network through a secondary Ethernet connection on your machine. See the documentation and man pages for `dip` for more information on this procedure.

SLIP is quite unlike Ethernet, in that there are only two machines on the ``network''---the SLIP host (that's you) and the SLIP server. For this reason, SLIP is often referred to as a ``point-to-point'' connection. A generalization of this idea, known as PPP (Point to Point Protocol) has also been implemented for Linux.

When you initiate a connection to a SLIP server, the SLIP server will give you an IP address based on (usually) one of two methods. Some SLIP servers allocate ``static'' IP addresses---in which case your IP address will be the same every time you connect to the server. However, many SLIP servers allocate IP addresses dynamically---in which case you receive a different IP address each time you connect. In general, the SLIP server will print the values of your IP and gateway addresses when you connect. `dip` is capable of reading these values from the output of the SLIP server login session and using them to configure the SLIP device.

Essentially, configuring a SLIP connection is just like configuring for loopback or ethernet. The main differences are discussed below. Read the previous section on configuring the basic TCP/IP files, and apply the changes described below.

- 5.3.3.1 Static IP address SLIP connections using dip
- 5.3.3.2 Static IP address SLIP connections using slattach
- 5.3.3.3 Dynamic IP address SLIP connections using dip

Next: 5.3.3.1 Static IP address Up: 5.3 Networking with TCP/IP Previous: 5.3.2.8 Trying it out