Commuting between several network profiles
Object of this article
We study here the case of a computer that must adapt to different network configurations. Typically, this is a laptop that commutes between the residential network, the business one, the clients' ones, and so on. Several changes, such as IP address, gateway and name-servers, are required to switch from a configuration (or profile) to an other. In addition, we might want to restart services or start various tasks before or after reconfiguration.
We are to present in this document different softwares that identify the network to which the computer is now connected and that reconfigure the machine accordingly. That is right, all this can happen automagically with no need for user intervention!
This document focuses on the Linux operating system in general and is based on software available from the Debian distribution in particular. Useful information may be found here if you are using another Linux distributions or even possibly for other Unix-like operating systems. This document will probably be of no utility to the Microsoft Windows system administrator, however.
This document is organized as follows: first, we present a detailed analysis of the problem, in order to isolate sub-problems and define terminology. Then, we draw a list of available softwares and compare them one at a time. Finally, we give our personal criteria and the list of packages that best suit them.
Our goal is to let the computer detect when its localization changes, to let it identify its new environment and adapt its configuration accordingly. This as a whole is our specifications and we may draw three different tasks, as described below.
- Detection of a potential change. Suspending or resuming the computer, plugging a network cable, connecting the computer to AC or docking it to a docking station, as well as adding a PCMCIA network card, are among the events that might provoke a change in the environment of the computer. Execution of the various tools described below will only be triggered on one of those events taking place. We call this task of detection of a potential change Task 1.
- Identification of current environment. At this phase, the computer will typically try and contact some "permanent" network equipments that could help it identify its current location, or that it is no longer connected to them. This task is labeled Task 3 through this document. The result of this phase will condition a potential reconfiguration at the next step.
- System reconfiguration, or Task 3. We may further distinguish
two aspects of this task:
- Reconfiguration of the network interfaces per se. At least,
this involves setting its IP address, tuning the
/etc/resolv.conffile (which stores name servers) and the routes. This will be our Task 3.a.
- Service reconfiguration, or even application reconfiguration (for instance, using a different HTTP proxy), and running commands that are specific to the new environment (such as synchronizing some files). We call this Task 3.b.
- Reconfiguration of the network interfaces per se. At least, this involves setting its IP address, tuning the
Warning: the following comparison of available softwares was performed in August 2003 and thus may not be completely up to date. Should a new package be featured or should a package deserve a revised description in this list, I would gladly update this document according to your input.
All softwares presented in this section are available from the
Debian GNU/Linux distribution. Debian has its own way to configure
network interfaces: the
ifupdown package provides
high-level tools to configure them based on the content of file
/etc/network/interfaces. That does not prevent you,
however, from using the more widely known command
ifconfig, possibly ignoring the
/etc/network/interfaces file. The benefit of such
solutions is their availability on systems other than Debian. As the
author only uses Debian, he shall give his preference to solutions
that integrate with the Debian way of managing network interfaces.
The Debian package
ifupdown provides a "mapping"
mechanism, which lets a script be called when "
<interface>" is issued. The output of this script will
determine what mapping to invoke. Typically, the script will identify
the environment of the computer. Its IP address and gateway will be
set according to the activated mapping. The
package lets you configure nameservers in a similar fashion. In
addition, it is possible to specify in the
/etc/network/interfaces file some actions to execute
after a specific mapping has been set up. The
package, in association with the
fulfills Task 3.a and provides the bare minimum (i.e. hooks) to run
the administrator's own scripts for Task 3.b.
resolvconf are specific to Debian (as far as the
author knows) and partially solves the issue at stake in this
document. Some of the softwares listed below integrate with them, some
Software for Task 1: Detection of a potential change
In order to detect when the computer suspends, stands by and
resumes, it is recommended to use APM or ACPI (which are mutually
exclusive) and to install the
package, respectively. Those packages let you run arbitrary scripts
when a change occurs, such as plugging to AC or suspending the
For a different matter,
ifplugd is a very simple daemon that
(by default) will run the command "
on plugging or unplugging the network cable. Let us mention that
laptop-net (described further below in this document) integrates
this functionality, but remains less robust:
ifplugd may for
instance ignore short disconnections of the network cable.
hotplug package allows you to detect when
a network card is inserted or ejected (typically a PCMCIA network
card) and to configure the corresponding interface.
Software for Task 2 (identification of current environment) and Task 3 (system reconfiguration)
A lot of packages are available from Debian for those two tasks. Some are limited to one of them, some handle both tasks. We shall review them in alphabetical order, but before starting, a warning: the judgements below reflect the author's opinion and only his. This is not the official position of the Debian project or anybody else's but the author's.
Divine: Automatic IP configuration detection for laptops
- Tasks 2 and 3.a, enables you to perform Task 3.b by hand.
- Only tests a remote IP (not MAC address).
ifupdown(does not update
- Does not support DHCP.
- Silly configuration file format.
- Self-defined as a "quick hack", raising security concerns.
- No reason to install it.
Guessnet: Guess which LAN is connected to a network device
- Task 2 only.
- Tests the IP address and optionally the MAC address of a remote machine, is also able to test the presence of a access concentrator (via a pppoe modem) (this needs more testing) and to run an arbitrary script. Provides a test to check whether the network cable is plugged.
- Designed for
ifupdown's mappings, thus supports everything
ifupdownsupports (static IP, DHCP, ...). Think to package
- Requires tricks to pass options to itself in file
/etc/network/interfaces. Legibility is decent.
- Leaves Task 3 up to
ifup(which performs Task 3.a and runs user-specified scripts for Task 3.b).
- Provides promising scripts (
test-wifi-ap, etc) but documentation is incomplete.
- Good, its only inconvenience is that it handles one interface at a time.
Ifscheme: scheme control for network interfaces
- Integrated to
ifupdown(lets you activate a specific mapping).
- Does nothing (assumes the environment has been identified, relies on
ifupdownto reconfigure the system) but merely activates a specific mapping among those described in file
- For those willing to reconfigure their network manually, but cleanly (a la Debian). Given our ambitions in this document, we have no reason to install that package.
ifupdown-roam: roaming enhancements for ifupdown
- Task 2 only.
- Designed for a roaming computer, its most interesting features have been
integrated to the
ifupdown-roam's author now recommends using
- No reason to install it.
intuitively: automatic IP configuration detection for laptops
- Tasks 2 and 3.a, with hooks to run your scripts for Task 3.b.
- Similar to
divine, only cleaner.
- Tests a remote machine's IP address and optionally its MAC address.
- Clean configuration file.
- Manual pages and README file.
- Uses symbolic links arranged in one tree of files per profile:
/etc/intuitively/profile_id/etc/resolv.conf -> /etc/resolv.conf.
- Does not support DHCP.
- Better than
divine, but still very much incomplete.
laptop-net: automatically adapt laptop ethernet
- The all-in-one: Tasks 1, 2 and 3.
- Integrated to
/etc/apmand detects changes of network link state (cable is plugged or unplugged).
- Only tests IP addresses (not MAC addresses).
- Supports DHCP.
- No manual page, no README, no time to lose to guess.
- As a bonus, leaves dead symbolic links upon desinstallation.
- Probably only used by its author, and that is good this way.
laptop-netconf: network detection and configuration program for laptops
- Task 2, enables you to perform Task 3 by hand.
- Only tests pairs of IP and MAC addresses.
- Runs a user-provided script on identifying a remote host.
- Only works for one interface, in all and for all!
- Self-proclaimed still in development.
- Little documentation: short man page, in addition to the documentation found in the configuration files.
- Suggests using symbolic links, one has to write ones own script to actually use them.
- Suggests luring
ifupdownby replacing the
- Not as mature and comprehensive as
netenv: configure your system for different network environments
- Task 3.a, enables you to perform Task 3.b by hand.
- Displays a text dialog box to let you choose the network configuration on boot(!). It may be skipped, too.
- Lets you do what
/etc/network/interfaces's mappings already do. Useless for Debian, unless you want the dialog box.
- Manual page and HTML documentation.
- No reason to install it (see rather
switchconf: change system configuration to one of many predefined
- Task 3.a, is rather tedious to setup for Task 3.b.
- Uses symbolic links, the same "elegant" way
- Suggests luring
ifupdownby replacing the
- Uses two folders, namely
after.d, where to put scripts (not included) that should be run before and after each configuration change. This is quite unpractical when one wants to run scripts only in some configurations: rather use "
up" lines in the
/etc/network/interfacesfile for that.
- No reason to install it.
waproamd: WLAN roaming daemon
- Designed for those IEEE 802.11 WiFi interfaces whose driver supports the Linux wireless extension.
- Tasks 1 and 2: for each interface, a daemon continuously checks whether an access point is in reach.
- A generic script (or an access point specific script, if existing) is
run when an access point is found or lost; this script will, typically, call
iwconfig, which in turn will handle Task 3.
- Used to cooperate with
ifplugd, but no longer needs it.
- Not terribly practical, but mandatory if you want to do with a WiFi
ifplugddoes for wire interfaces, namely detecting access point presence and automatically configuring the interface with no human intervention. Note, however, that given the extra battery consumption induced by the continuous use of the WiFi card, the user of a laptop not plugged on AC might prefer manually switch the WiFi card off and only turn it on when an access point is actually available.
whereami: automatically reconfigure your (laptop) system for a new location
- Tasks 2 and 3.a, provides several scripts for 3.b.
- Impressive as to situation identification: tests an IP or MAC address,
the response to a DHCP request, the presence of a network cable, of a PPPOE
access concentrator, of a pattern in "
lspci -v"'s output (to detect a docking station), of a kernel module being loaded ("
lsmod"), of a WiFi access point, and lastly it can test whether bytes were received on the interface.
- Lets you cascade tests, as well as test several interfaces successively: the provided sample configuration files are hideously complicated but show that virtually all situations can be described and handled.
- Typically ignores the
/etc/network/interfacefile. It seems that you have to reconfigure the IP by hand(!).
- Runs any number of scripts when one arrives to, leaves or simply is in a specific situation.
- Provides scripts to adapt
masqmail, Netscape's configuration file, the
qmail's smarthost, the timezone, ...
- Optionally integrated to APM.
- Manual pages and HTML documentation (not perfectly up to date).
- In the end,
whereamiis impressive for Task 2, a bit weak for Task 3.a and flexible and handy to the extreme, thanks to its scripts, for Task 3.b.
whereamicannot solve your roaming configuration problem, no other package will do. Now, you may be able to get out of it with something a tiny bit simpler than
In this section, we shall present the author's particular setup and motivate his software choices. In the following case study, the laptop computer commutes between a residential network and a professional one and only possesses a single permanent network interface (as opposed to removable PCMCIA cards). On top of fullfiling our specifications, the author would like the chosen solution to:
- integrate with the Debian way of managing network interfaces, as opposed
ifupdownand directly modifying the interfaces;
- comply with the "Unix philosophy", as summarized by "one task per tool".
Therefore, the author selected:
- For Task 1 (detection of a potential change), packages
ifplugdis the natural choice for detecting the network cable being plugged or unplugged, and the choice of
apmdwas forced by the use of the APM system as the power management system (should the author use the ACPI system, he would have installed the
- For Task 2 (identification of the current environment), package
guessnet. It provides a sufficient set of tests and is well integrated to
- For Task 3.a (network interface reconfiguration):
/etc/network/interfaces's mappings, as suggested by package
ifupdown, and using package
resolvconfto handle the
/etc/resolv.conffile (name resolution).
- For Task 3.b (service reconfiguration):
/etc/network/interfacesfile, lines that only contain very simple commands for now. Nevertheless, the author kept a copy of those scripts provided by package
whereamifor a possible future use.
guessnet packages required no particular reconfiguration. The
whole roaming configuration is described, in a compact and rather clear
manner, in the
/etc/network/interfaces file, of which extracts
are presented in appendix as an example.
Guessnet is thus our preferred solution to our roaming problem,
for its by-design integration to the Debian way to manage network interfaces
and for its rich functionality (numerous tests, multiple physical interface
support, ...). For more complicated cases, especially where it is necessary to
cascade tests or to test several physical interfaces at one,
whereami seems to be the only contender.
The author wishes to thank first and foremost all contributors, let them be developers, users or translators, to the Debian project for providing to the largest number a large set of quality software. Thanks also go the debian-user-french mailing-list's contributors, in particular François Tourde and Loïc Minier.
Extracts from the author's
mapping eth0 script /usr/sbin/guessnet-ifupdown map default: none map verbose: true iface eth0-limsi inet static # Interface configuration, usual part address 192.44.xx.yy (hidden) netmask 255.255.255.0 broadcast 184.108.40.206 gateway 220.127.116.11 # Lines for resolvconf dns-search limsi.fr dns-nameservers 18.104.22.168 22.214.171.124 126.96.36.199 # Test definitions, for guessnet test1-peer address 188.8.131.52 mac aa:bb:cc:dd:ee:ff (hidden) test2-peer address 184.108.40.206 mac aa:bb:cc:dd:ee:ff (hidden) # Adapting default printer up foomatic-configure -n biglexrv -D iface eth0-family inet static address 192.168.2.26 netmask 255.255.255.0 broadcast 192.168.2.255 gateway 192.168.2.22 dns-search family dns-nameservers 192.168.2.22 test-peer address 192.168.2.1 mac aa:bb:cc:dd:ee:ff (hidden) up foomatic-configure -n CanonS600 -D
Copyright Daniel Déchelotte, 2004-2005.
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