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Networkd is the network configuration component of the systemd software suite. It is well integrated into NixOS below <code>systemd.network</code> and should be preferred over <code>networking.interfaces</code> options for most use cases, since it receives far superior maintenance.
{{Systemd/breadcrumb}}
{{DISPLAYTITLE:systemd-networkd}}
[https://www.freedesktop.org/software/systemd/man/systemd-networkd.html systemd-networkd] is the network configuration component of the [[systemd]][[Category:systemd]] software suite. It is well integrated into NixOS below {{Nixos:option|systemd.network}} and should be preferred over {{Nixos:option|networking.interfaces}} options for most use cases, since it receives far superior maintenance.


Configuration for networkd is split into three sections.
Configuration for networkd is split into three sections.


* <code>systemd.network.links</code> reconfigures existing network devices
* {{Nixos:option|systemd.network.links}} reconfigures existing network devices
** https://www.freedesktop.org/software/systemd/man/systemd.link.html
** https://www.freedesktop.org/software/systemd/man/systemd.link.html
** actually implemented by udev, not networkd
** actually implemented by udev, not networkd
* <code>systemd.network.netdevs</code> creates virtual network devices
* {{Nixos:option|systemd.network.netdevs}} creates virtual network devices
** https://www.freedesktop.org/software/systemd/man/systemd.netdev.html
** https://www.freedesktop.org/software/systemd/man/systemd.netdev.html
* <code>systemd.network.networks</code> configures network devices
* {{Nixos:option|systemd.network.networks}} configures network devices
** https://www.freedesktop.org/software/systemd/man/systemd.network.html
** https://www.freedesktop.org/software/systemd/man/systemd.network.html


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== Basics ==
== Basics ==
=== When to use ===
Use systemd-networkd for setups that rely on static configuration, that doesn't change much during its lifetime, that does not require varying profiles for a single interface. Common examples are:
* Servers/Routers
* Always-On VPN Tunnels
Following that logic, it is less suitable to
* Varying WLAN profiles
* Selectively used VPN tunnels
These use cases are better served by [[NetworkManager]] and its various frontends, that provides a better integrated user experience for various desktop systems.
{{Note|Both systemd-networkd and NetworkManager can exist in parallel on the same machine,
when they manage a distinct set of interfaces.}}
=== Enabling ===
=== Enabling ===


To be able to use networkd configuration it needs to be enabled first.
To be able to use networkd configuration, it needs to be enabled first.


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
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</syntaxhighlight>
</syntaxhighlight>


Some guides will mention the <code>networking.useNetworkd</code> option, which
Some guides will mention the {{Nixos:option|networking.useNetworkd}} option, which
offers translation of some <code>networking.*</code> options into networkd. If you
in addition to enabling systemd-networkd, also offers translation of some  
can write your complete network setup in native networkd configuration, you should
{{Nixos:option|networking.interfaces}} and {{Nixos:option|networking.useDHCP}} options
stay away from that option.
into networkd.
If you can write your complete network setup in native networkd configuration, you
should stay away from that option.


=== Configuring ===
=== Configuring ===
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interface stored in <code>/etc/systemd/network</code>.
interface stored in <code>/etc/systemd/network</code>.


The following configuration in your NixOS configuration
The following declaration in your NixOS configuration


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
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</nowiki>}}
</nowiki>}}


Note that we usually prefix the configuration file with a number. This can be important,
Note that we usually prefix the configuration file with a number. This can be important, because networkd collects all available configuration files, then sorts them alphanumerically, and uses the first match for each interface as its configuration. This happens separately for <code>.link</code>, <code>.netdev</code> and <code>.network</code> files, so that you can have one configuration of each type per interface.
because networkd collects all available configuration files, then sorts them alphabetically,
 
and uses the first match for each interface as its configuration. This happens separately
=== Debugging ===
for <code>.link</code>, <code>.netdev</code> and <code>.network</code> files, so
 
that you can have one configuration of each type per interface.
When things don't work as expected, the journal for <code>systemd-networkd.service</code> should be consulted. Unfortunately, by default the log is not very useful in its default loglevel. Increasing the loglevel can be done using the <code>SYSTEMD_LOG_LEVEL</code> environment variable.
 
<syntaxhighlight lang="nix">
systemd.services."systemd-networkd".environment.SYSTEMD_LOG_LEVEL = "debug";
</syntaxhighlight>


=== Limitations ===
=== Limitations ===
Some limitations might be surprising, so it is probably helpful to get them out of the
way early.


* <code>systemd.network.links</code> only gets applied at boot time
Some limitations might be surprising, so it is probably helpful to get them out of the way early.
* <code>systemd.network.netdevs</code> does not modify existing network interfaces
** https://github.com/systemd/systemd/issues/9627


Interfaces are set up in a one-shot fashion with networkd. That means it sets them up
* {{Nixos:option|systemd.network.links}}
once and doesn't expect them to change significantly during their lifetime.
** Executed by udev and only applied on boot
 
* {{Nixos:option|systemd.network.netdevs}}
This means that networkd is not well suited to manage scenarios where multiple profiles
** Does not modify properties (e.g., MTU, VLAN ID, VXLAN ID, Wireguard Peers) of existing netdevs
can be configured onto an interface, or an interface is only selectively up. This is mostly
*** https://github.com/systemd/systemd/issues/9627
the case for WLAN on mobile devices, and occassional usage of VPN tunnels. Use
[[Networkmanager]] to cover these use cases, it can run in paralle with networkd, as
long as they aren't set up to manage the same interfaces.


=== network-online.target ===
=== network-online.target ===
Line 101: Line 118:


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
systemd.network."50-enp3s0" = {
systemd.network.networks."50-enp3s0" = {
   matchConfig.Name = "enp3s0";
   matchConfig.Name = "enp3s0";
   # acquire a DHCP lease on link up
   # acquire a DHCP lease on link up
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entirely, because a working <code>network-online.target</code> is required for some
entirely, because a working <code>network-online.target</code> is required for some
services to properly start without race conditions.
services to properly start without race conditions.
Also consider enabling the <code>systemd.network.wait-online.anyInterface</code> option,
which makes networkd consider the network online when any interface is online,
as opposed to all that have a positive value for <code>linkConfig.RequiredForOnline</code>.
This is useful on portable machines with a wired and a wireless interface, for example.


Recommended documentation:
Recommended documentation:
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     matchConfig.Name = "enp1s0";
     matchConfig.Name = "enp1s0";
     networkConfig = {
     networkConfig = {
      # start a DHCP Client for IPv4 Addressing/Routing
       DHCP = "ipv4";
       DHCP = "ipv4";
      # accept Router Advertisements for Stateless IPv6 Autoconfiguraton (SLAAC)
       IPv6AcceptRA = true;
       IPv6AcceptRA = true;
     };
     };
     # making routing on this interface a dependency for network-online.target
     # make routing on this interface a dependency for network-online.target
     linkConfig.RequiredForOnline = "routable";
     linkConfig.RequiredForOnline = "routable";
   };
   };
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     matchConfig.Name = "enp1s0";
     matchConfig.Name = "enp1s0";
     address = [
     address = [
        # configure addresses including subnet mask
      # configure addresses including subnet mask
        "192.0.2.100/24"
      "192.0.2.100/24"
        "2001:DB8::2/64"
      "2001:DB8::2/64"
     ];
     ];
     routes = [
     routes = [
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       { routeConfig.Gateway = "192.0.2.1"; }
       { routeConfig.Gateway = "192.0.2.1"; }
       # or when the gateway is not on the same network
       # or when the gateway is not on the same network
       { routeConfig = {
       {
        Gateway = "172.31.1.1";
        routeConfig = {
        GatewayOnLink = true;
          Gateway = "172.31.1.1";
      }; }
          GatewayOnLink = true;
        };
      }
     ];
     ];
     # make the routes on this interface a dependency for network-online.target
     # make the routes on this interface a dependency for network-online.target
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VLANs can be configured on top of hardlinks as well as virtual links, like bonding interfaces. They provide separate logical networks over physical links.
VLANs can be configured on top of hardlinks as well as virtual links, like bonding interfaces. They provide separate logical networks over physical links.


In this example we tag two VLANs with Ids 10 and 20 on a physical link <code>enp1s0</code>. The VLAN interfaces become available <code>vlan10</code> and <code>vlan20</code> and can receive additional configuration.
In this example we tag two VLANs with Ids 10 and 20 on a physical link <code>enp1s0</code>. The VLAN interfaces become available as <code>vlan10</code> and <code>vlan20</code> and can receive additional configuration.


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
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         # tag vlan on this link
         # tag vlan on this link
         vlan = [
         vlan = [
           vlan10
           "vlan10"
           vlan20
           "vlan20"
         ];
         ];
        networkConfig.LinkLocalAddressing = "no";
        linkConfig.RequiredForOnline = "carrier";
       };
       };
       "40-vlan10" = {
       "40-vlan10" = {
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       };
       };
     };
     };
  };
</syntaxhighlight>
=== Bridge ===
Given multiple interfaces, that are connected into a bridge will act like a common switch and forward Ethernet frames between all connected bridge ports. The Linux bridge supports various features, like spanning tree, bridge port isolation or acting as a multicast router.
The configuration on top of the bridge interface depends on the desired functionality, e.g., configuring an IP address would make the bridge host reachable on the Ethernet segment.
Recommended documentation:
* [https://www.freedesktop.org/software/systemd/man/systemd.network.html#%5BBridge%5D%20Section%20Options <nowiki>[Bridge]</nowiki> configuration reference]
<syntaxhighlight lang="nix">
  systemd.network = {
    netdevs = {
      # Create the bridge interface
      "20-br0" = {
        netdevConfig = {
          Kind = "bridge";
          Name = "br0";
        };
      };
    };
    networks = {
      # Connect the bridge ports to the bridge
      "30-enp1s0" = {
        matchConfig.Name = "enp1s0";
        networkConfig.Bridge = "br0";
        linkConfig.RequiredForOnline = "enslaved";
      };
      "30-enp2s0" = {
        matchConfig.Name = "enp2s0";
        networkConfig.Bridge = "br0";
        linkConfig.RequiredForOnline = "enslaved";
      };
      # Configure the bridge for its desired function
      "40-br0" = {
        matchConfig.Name = "br0";
        bridgeConfig = {};
        # Disable address autoconfig when no IP configuration is required
        #networkConfig.LinkLocalAddressing = "no";
        linkConfig = {
          # or "routable" with IP addresses configured
          RequiredForOnline = "carrier";
        };
      };
    };
  };
</syntaxhighlight>
</syntaxhighlight>


=== Bonding ===
=== Bonding ===


Given two hardlinks <code>enp2s0</code> and <code>enp3s0</code> create a virtual <code>bond0</code> interface using Dynamic LACP (802.3ad), hashing outgoing packets using a packet's Layer3/4 (OSI Layer) information.
Given two hardlinks <code>enp2s0</code> and <code>enp3s0</code> create a virtual <code>bond0</code> interface using Dynamic LACP (802.3ad), hashing outgoing packets using a packet's layer 3/4 (network/transport layer in the OSI model) information.


<syntaxhighlight lang="nix">
<syntaxhighlight lang="nix">
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   };
   };
</syntaxhighlight>
</syntaxhighlight>
=== Router Advertisement ===
Router advertisements are way to allow clients to achieve stateless autoconfiguration (SLAAC). The most prominent setup is where the router announces a prefix onto a LAN segment, which the receiving client can use to set up an address on that prefix, and configure the sender as its default gateway.
In this example the router will announce a static IPv6 prefix on the <code>lan</code> interface from it's automatically configured link local address on that link. The router does not generally require a unique local or globally reachable address on the link, unless you also want to host services like DNS and NTP on that LAN segment.
Recommended documentation:
* [https://www.freedesktop.org/software/systemd/man/systemd.network.html#%5BIPv6SendRA%5D%20Section%20Options <nowiki>[IPv6SendRa]</nowiki> configuration reference]
<syntaxhighlight lang="nix">
  systemd.network = {
    networks = {
      "30-lan" = {
        matchConfig.Name = "lan";
        address = [ "2001:db8:1122:3344::1/64" ];
        networkConfig = {
          IPv6SendRA = true;
        };
        ipv6Prefixes = [
          {
            # Announce a static prefix
            ipv6PrefixConfig.Prefix = "2001:db8:1122:3344::/64";
          }
        ];
        ipv6SendRAConfig = {
          # Provide a DNS resolver
          EmitDNS = true;
          DNS = "2001:db8:1122:3344::1";
        };
      };
    };
  };
</syntaxhighlight>
An extended form of this setup uses DHCPv6 prefix delegation to acquire a dynamic prefix over a WAN link, which then gets distributed onto designated LAN segments.
=== WireGuard ===
WireGuard can also be set up using <code>systemd.network.netdevs</code>. More details can be found at [[WireGuard#Setting up WireGuard with systemd-networkd]].


== User configurations ==
== User configurations ==
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* [https://gist.github.com/mweinelt/b78f7046145dbaeab4e42bf55663ef44 NixOS 22.11 VDSL Router (VLANs on top of Bonding, IPv6 Prefix-Delegation, pppd Integration)] by [https://github.com/mweinelt mweinelt]
* [https://gist.github.com/mweinelt/b78f7046145dbaeab4e42bf55663ef44 NixOS 22.11 VDSL Router (VLANs on top of Bonding, IPv6 Prefix-Delegation, pppd Integration)] by [https://github.com/mweinelt mweinelt]


[[Category: Networking]]
[[Category:systemd]]
[[Category:Networking]]
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