that you only have to invoke a simple command that performs all steps shown above...

Odnośniki

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

This is what dip is for. The current release as of this writing is version 3.3.7. It has been patched 2
very heavily by a number of people, so that you can't speak of the dip program anymore.
These dierent strains of development will hopefully be merged in a future release.
dip provides an interpreter for a simple scripting language that can handle the modem for
you, convert the line to SLIP mode, and congure the interfaces. This is rather primitive
and restrictive, but sucient for most cases. A new release of dip may feature a more
versatile language one day.
To be able to congure the SLIP interface, dip requires root privilege. It would now be
tempting to make dip setuid to root, so that all users can dial up some SLIP server without having to give them root access. This is very dangerous, because setting up bogus interfaces and default routes with dip may disrupt routing on your network badly. Even worse, this
will give your users the power to connect to any SLIP server, and launch dangerous attacks on your network. So if you want to allow your users to re up a SLIP connection, write
small wrapper programs for each prospective SLIP server, and have these wrappers invoke
dip with the specic script that establishes the connection. These programs can then safely be made setuid root.3
7.3.1 A Sample Script
A sample script is produced in gure 7.1. It can be used to connect to cowslip by
invoking dip with the script name as argument:
# dip cowslip.dip
DIP: Dialup IP Protocol Driver version 3.3.7 (12/13/93)
Written by Fred N. van Kempen, MicroWalt Corporation.
connected to cowslip.moo.com with addr 193.174.7.129
#
After connecting to cowslip and enabling SLIP, dip will detach from the terminal and
go to the background. You can then start using the normal networking services on the
SLIP link. To terminate the connection, simply invoke dip with the -k option. This sends
a hangup signal to dip process, using the process id dip records in /etc/dip.pid:4
2
dip means Dialup IP. It was written by Fred van Kempen.
3
diplogin can (and must) be run setuid, too. See the section at the end of this chapter.
4
See the newsgroup alt.tla for more palindromic fun with three-letter acronyms.
7.3. Using dip
124
# Sample dip script for dialing up cowslip
# Set local and remote name and address
get $local vlager
get $remote cowslip
port cua3
# choose a serial port
speed 38400
# set speed to max
modem HAYES
# set modem type
reset
# reset modem and tty
flush
# flush out modem response
# Prepare for dialing.
send ATQ0V1E1X1\r
wait OK 2
if $errlvl != 0 goto error
dial 41988
if $errlvl != 0 goto error
wait CONNECT 60
if $errlvl != 0 goto error
# Okay, we're connected now
sleep 3
send \r\n\r\n
wait ogin: 10
if $errlvl != 0 goto error
send Svlager\n
wait ssword: 5
if $errlvl != 0 goto error
send hey-jude\n
wait running 30
if $errlvl != 0 goto error
# We have logged in, and the remote side is firing up SLIP.
print Connected to $remote with address $rmtip
default
# Make this link our default route
mode SLIP
# We go to SLIP mode, too
# fall through in case of error
error:
print SLIP to $remote failed.
Figure 7.1: A sample dip script
7.3. Using dip
125
# kill -k
In dip's scripting language, keywords prexed with a dollar symbol denote variable
names. dip has a predened set of variables which will be listed below. remote and local,
$
$
for instance, contain the hostnames of the local and remote host involved in the SLIP link.
The rst two statements in the sample script are get commands, which is dip's way
to set a variable. Here, the local and remote hostname are set to vlager and cowslip,
respectively.
The next ve statements set up the terminal line and the modem. The reset sends a
reset string to the modem; for Hayes-compatible modems, this is the ATZ command. The
next statement ushes out the modem response, so that the login chat in the next few lines
will work properly. This chat is pretty straight-forward: it simply dials 41988, the phone number of cowslip, and logs into the account Svlager using the password hey-jude. The
wait command makes dip wait for the string given as its rst argument; the number given
as second argument make the wait time out after that many seconds if no such string is