170 lines
6.8 KiB
Markdown
170 lines
6.8 KiB
Markdown
NetworkManager daemon
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=====================
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The following diagram describes the main components of the
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NetworkManager daemon. Note that each component is in most cases a
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GObject and the names always start with the "NM" prefix, which has
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been omitted for clarity.
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## Manager
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The main responsibilities of the manager are:
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- initialize all known device factories. A device factory contains the
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logic detect new devices of a certain type and create the
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corresponding object;
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- maintain a list of devices created by the factories;
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- maintain a list of active connections;
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- expose on D-Bus properties, methods and signal on the
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`/org/freedesktop/NetworkManager`
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[object](../../introspection/org.freedesktop.NetworkManager.xml).
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## Policy
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This object implements some policy decisions that involve multiple
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connection profiles, such as:
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- it determines what is the best (with lowest metric) active
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connection with default route for IPv4 and IPv6;
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- it updates the DNS configuration in the DNS manager, also according
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to what connection has the best default route;
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- it handles the activation of secondary connections when a
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connection goes up (see property `connection.secondaries` in
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`man nm-settings`);
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- it collects IPv6 prefix delegations from active connections, to
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distribute them on connections using IPv6 shared mode;
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## Settings
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This object handles connection profiles; each profile is represented
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as a *SettingsConnection* object and is persisted to disk using one of
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the existing *SettingsPlugin*s such as keyfile, ifcfg-rh or
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ifupdown.
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It also controls *SecretAgent*s; an agent is an external service that
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registers to NetworkManager as capable of handling requests for new
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secrets. For example, when a Wi-Fi connection is activated and the
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password is missing or wrong, NetworkManager asks all registered
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agents for the missing secrets and then continues with
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activation. Examples of tools that register as agents are: nmcli,
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nmtui, GNOME shell, the GTK nm-applet and the KDE network applet.
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## Devices and device factories
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As mentioned before, NetworkManager instantiates device factories to
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discover and create new devices. Those factories are internal to the
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daemon or provided by a device plugin; a plugin is a dynamic library
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(shared object) that is loaded at runtime. NetworkManager uses plugins
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for optional functionality that depend on external software. In this
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way, it is possible to install a minimal version of NetworkManager
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with a limited set of dependencies. As there is no stable API/ABI for
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those plugins, they must be built together with the daemonq and
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maintained as part of NetworkManager.
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Currently the following device types are provided by plugins:
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- Wi-Fi (depends on wpa_supplicant)
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- OVS (depends on openswitch)
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- PPP (depends on pppd)
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- Bluetooth (depends on bluez)
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- team (depends on teamd)
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When a device is activated, it relies on other objects:
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- *L3cfg*: controls the IP configuration (address, routes, etc) on a
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given ifindex, and also does IPv4 ACD (address conflict detection,
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also know as DAD - duplicate address detection);
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- *DhcpClient*: performs DHCPv4 and DHCPv6 on the interface; the
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object has different implementations;
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- *NDisc*: implements IPv6 SLAAC (stateless address
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autoconfiguration, RFC 4861 and 4862); it supports acting both as
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a host or a router for shared IPv6 mode;
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- *LldpListener*: when the profile enables
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[LLDP](https://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol)
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via the `connection.lldp` property, this object sets up a socket
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to listen for neighbors;
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- *FirewalldManager*: talks with [firewalld](https://firewalld.org/)
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to set the interface in the zone specified by the
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`connection.zone` property;
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- *BondManager*: used to configure bond devices in a special mode
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(balance-slb) that requires the creation of nftables rules;
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For more information about the implementation of devices, see [this
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document](./device.md).
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## Platform
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*Platform* communicates with kernel to query and update the
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configuration of network interfaces; it uses netlink and implements
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the crafting and parsing of netlink message by itself without relying
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on external libraries such as libnl.
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Platform has two subclasses, *PlatformLinux* and a *PlatformFake*. The
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former is the one that contain the actual implementation while the
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latter is only used for unit testing.
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Note how the platform object has an incoming dotted arrow in the
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diagram, to represent that the object is used by several other
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objects.
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As mentioned, the purposes of platform are:
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- perform operations such as adding or removing links, addresses,
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routes, routing rules and other kernel entities
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- allow querying the current state of the kernel configuration. To do
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so, platform listens to kernel notifications and parses them to
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build a cache of `NMPObject`s that is always up to date.
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NMPObject and its subtypes are also used through the core to represent
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information about addresses, routes, etc. Thus the cache of NMPlatform
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contains the currently configured objects in the netlink API, while
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other NMPObject instances are used for other tracking purposes.
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For these purposes platform uses two sockets, one with protocol
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NETLINK_ROUTE for regular operations about links, addresses, routes,
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etc. and a NETLINK_GENERIC socket to configure Wireguard and MPTCP.
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## Other objects
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The diagram shows other objects on the right side:
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- *DnsManager*: merges all the DNS data received by multiple
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interfaces and updates the system configuration. Besides directly
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writing `/etc/resolv.conf`, it supports updating
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`systemd-resolved` and `dnsmasq` via plugins.
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- *HostnameManager*: implements reading and updating the system
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hostname; by default it tries to do that by talking to
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[systemd-hostnamed](https://www.freedesktop.org/wiki/Software/systemd/hostnamed/)
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via D-Bus; in case it's not available, the hostname manager falls
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back to reading and writing `/etc/hostname` directly.
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- *RfkillManager*: enumerates RFKill devices and controls their status. See also
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the [related page](https://networkmanager.dev/docs/rfkill/) on the website.
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- *AuthManager*: is used to authenticate the API requests received by
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the daemon. The authentication is done via
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[Polkit](https://www.freedesktop.org/software/polkit/docs/latest/polkit.8.html)
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- *DbusManager*: creates a connection to the system D-Bus instance
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and allows exporting objects
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- *SleepMonitor*: gets notifications for sleep and wake events by
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registering to the available subsystem provided by the distro such
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as systemd-logind, upower or ConsoleKit.
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- *SessionMonitor*: tracks which users have an active session by
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using systemd-logind, elogind or ConsoleKit.
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- *Dispatcher*: takes care of spawning dispatcher scripts by talking
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to the `nm-dispatcher` service via D-Bus.
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