| Previous | Table of Contents | Next |
Steve Burnett
The Linux kernel supports two serial-line protocols for transmitting Internet Protocol (IP) traffic: SLIP (Serial Line Internet Protocol) and PPP (Point-to-Point Protocol). These protocols were developed as a poor man’s alternative to expensive leased-line setups for getting Internet connectivity. Anyone with a reasonably high-speed modem and a service provider that supports these protocols can get their Linux machine IP-connected for a very low cost compared to leased-line systems. SLIP drivers for Linux were available soon after Linux was first released, and PPP support was added shortly thereafter. Although PPP has come to dominate the industry, the SLIP configuration is still helpful as a basis.
You need to make sure that a few things are set up in your Linux kernel or configuration files. TCP/IP networking must be enabled and the loopback interface should be configured.
See “Configuring the Software Loopback Interface,” p. 448
You’ll want the IP address of your Domain Name Service (DNS) server to be included in your /etc/resolv.conf file to make accessing other machines besides your dial-up host convenient. If your dial-up link is slow or error-prone, you might want to run a name server on your Linux box, to cache any DNS lookups and decrease the amount of DNS IP traffic on your dial-up link.
See “The /etc/resolv.conf File,” p. 505
See “Using the named Daemon to Set Up the Server,” p. 506
Linux offers a number of programs to manage your SLIP operations. dip, the Dial-Up IP Protocol driver, is one of the most versatile tools. It provides a scripting language for automating control of the modem and automatically sets up the SLIP network interface and kernel routing tables. You can use dip to initiate SLIP connections or provide dial-up SLIP service to other machines. The syntax for dip is as follows:
dip [-tvi] [-m mtu] [scriptfile]
Table 29.1 describes dip’s most common command-line arguments.
| Argument | Description |
|---|---|
| -a | Prompts the user for username and password. |
| -t | Runs dip in command mode. Command mode gives you full access to everything dip can do, allowing you to initiate a SLIP connection manually. |
| -v | Used with -t to display the current error level. |
| -i | Tells dip to operate in input mode. This flag is used when dip provides SLIP service for others dialing into your machine. |
| -m mtu | Forces dip to use the specified MTU value. |
| scriptfile | Specifies the name of the dip script to run. |
Invoking dip with the -t option places it in command mode. This mode lets you control dip directly and is an excellent tool for developing and debugging dip scripts. The following shows you what dip’s command mode looks like:
$ /sbin/dip -t DIP: Dialup IP Protocol Driver version 3.3.7i-uri (17 Apr 95) Written by Fred N. van Kempen, MicroWalt Corporation. DIP>
| Previous | Table of Contents | Next |