June 2000
Intermediate to advanced
512 pages
15h 18m
English
Content preview from Linux Network Administrator's Guide, Second EditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Using dip
Now that was rather simple. Nevertheless, you might want to automate the steps previously described. It would be much better to have a simple command that performs all the steps necessary to open the serial device, cause the modem to dial the provider, log in, enable the SLIP line discipline, and configure the network interface. This is what the dip command is for.
dip means Dialup IP. It was
written by Fred van Kempen and has been patched very heavily by a
number of people. Today there is one strain that is used by almost
everyone: Version dip337p-uri, which is included
with most modern Linux distributions, or is available from the
metalab.unc.edu FTP archive.
dip provides an interpreter for a simple scripting language that can handle the modem for you, convert the line to SLIP mode, and configure the interfaces. The script language is powerful enough to suit most configurations.
To be able to configure 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, though, because setting up bogus interfaces and default routes with dip may disrupt routing on your network. Even worse, this action would give your users power to connect to any SLIP server and launch dangerous attacks on your network. If you want to allow your users to fire up a SLIP connection, write small wrapper programs for each prospective SLIP server ...
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