Commit 7eb45597 authored by Dan Williams's avatar Dan Williams

Update the readme

git-svn-id: 4912f4e0-d625-0410-9fb7-b9a5a253dbdc
parent 9fd459f3
THEORY OF OPERATION: Networking that Just Works
NetworkManager attempts to keep an active network connection available at all NetworkManager attempts to keep an active network connection available at all
times. The point of NetworkManager is to make networking configuration and times. The point of NetworkManager is to make networking configuration and
setup as painless and automatic as possible. If using DHCP, NetworkManager is setup as painless and automatic as possible. NetworkManager is intended to
_intended_ to replace default routes, obtain IP addresses from a DHCP server, replace default route, replace other routes, set IP addresses, and in general
and change nameservers whenever it sees fit. In effect, the goal of configure networking as NM sees fit (with the possibility of manual override as
NetworkManager is to make networking Just Work. If you have special needs, necessary). In effect, the goal of NetworkManager is to make networking Just
we'd like to hear about them, but understand that NetworkManager is not Work with a minimum of user hassle, but still allow customization and a high
intended to serve the needs of all users. level of manual network control. If you have special needs, we'd like to hear
about them, but understand that NetworkManager is not intended for every
From a list of all adapters currently installed on the system, NetworkManager
will first try a wired and then a wireless adapter. Wireless adapters that NetworkManager will attempt to keep every network device in the system up and
support wireless scanning are preferred over ones that cannot. NetworkManager active, as long as the device is available for use (has a cable plugged in,
does not try to keep a connection up as long as possible, meaning that plugging the killswitch isn't turned on, etc). Network connections can be set to
into a wired network will switch the connection to the wired network away from 'autoconnect', meaning that NetworkManager will make that connection active
the wireless one. whenever it and the hardware is available.
For wireless networking support, NetworkManager keeps a list of wireless "Settings services" store lists of user- or administrator-defined "connections",
networks, the preferred list. Preferred Networks are wireless networks that which contain all the settings and parameters required to connect to a specific
the user has explicitly made NetworkManager associate with at some previous network. NetworkManager will _never_ activate a connection that is not in this
time. So if the user walks into a Starbucks and explicitly asks NetworkManager list, or that the user has not directed NetworkManager to connect to.
to associate with that Starbucks network, NetworkManager will remember the
Starbucks network information from that point on. Upon returning to that
Starbucks, NetworkManager will attempt to associate _automatically_ with the How it works:
Starbucks network since it is now in the Preferred Networks list. The point of
this is to ensure that only the user can determine which wireless networks to The NetworkManager daemon runs as a privileged service (since it must access
associate with, and that the user is aware which networks are security risks and control hardware), but provides a D-Bus interface on the system bus to
and which are not. allow for fine-grained control of networking. NetworkManager does not store
connections or settings, it is only the mechanism by which those connections
are selected and activated.
To store pre-defined network connections, two separate services, the "system
NetworkManager runs as a root-user system level daemon, since it settings service" and the "user settings service" store connection information
must manipulate hardware directly. It communicates over DBUS with a and provide these to NetworkManager, also via D-Bus. Each settings service
desktop-level per-user process, nm-applet. Since Preferred Networks are can determine how and where it persistently stores the connection information;
user-specific, there must be some mechanism of getting this information for example, the GNOME applet stores its configuration in GConf, and the system
per-user. NetworkManager cannot store that information as it is user-specific, settings service stores it's config in distro-specific formats, or in a distro-
and therefore communicates over DBUS to the user daemon which provides those agnostic format, depending on user/administrator preference.
lists. NetworkManager also provides an API over DBUS for any DBUS-aware
application to determine the current state of the network, including available A variety of other system services are used by NetworkManager to provide
wireless networks the computer is aware of and specific details about those network functionality: wpa_supplicant for wireless connections and 802.1x
networks. This API also provides the means for forcing NetworkManager to wired connections, pppd for PPP and mobile broadband connections, DHCP clients
associate with a specific wireless network. Use of DBUS allows separation of for dynamic IP addressing, dnsmasq for proxy nameserver and DHCP server
NetworkManager, which requires no user-interface, and the parts of the user functionality for internet connection sharing, and avahi-autoipd for IPv4
interface which might be desktop environment specific. link-local addresses. Most communication with these daemons occurs, again,
via D-Bus.
The nm-applet provides a DBUS service called NetworkManagerInfo, which should
provide to NetworkManager the Preferred Networks lists upon request. It also
should be able to display a dialog to retrieve a WEP/WPA key or passphrase from Why doesn't my network Just Work?
the user when NetworkManager requests it. The GNOME version of
NetworkManagerInfo, for example, stores Preferred Networks in GConf and Driver problems are the #1 cause of why NetworkManager sometimes fails to
WEP/WPA keys in gnome-keyring, and proxies that information to NetworkManager connect to wireless networks. Often, the driver simply doesn't behave in a
upon request. consistent manner, or is just plain buggy. NetworkManager supports _only_
those drivers that are shipped with the upstream Linux kernel, because only
those drivers can be easily fixed and debugged. ndiswrapper, vendor binary
drivers, or other out-of-tree drivers may or may not work well with
NetworkManager, precisely because they have not been vetted and improved by the
open-source community, and becuase problems in these drivers usually cannot
be fixed.
Sometimes, command-line tools like 'iwconfig' will work, but NetworkManager will
fail. This is again often due to buggy drivers, becuase these drivers simply
aren't expecting the dynamic requests that NetworkManager and wpa_supplicant
make. Driver bugs should be filed in the bug tracker of the distribution being
run, since often distributions customize their kernel and drivers.
Sometimes, it really is NetworkManager's fault. If you think that's the case,
please file a bug at and choose the NetworkManager
component. Attaching the output of /var/log/messages or /var/log/daemon.log
(wherever your distribution directs syslog's 'daemon' facility output) is often
very helpful, and (if you can get) a working wpa_supplicant config file helps
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