systemd-networkd is a network manager that comes built in with Systemd. It has features, similar to NetworkManager and ConnMan which are more commonly used in distributions like Ubuntu and Fedora.

My old system

I had moved away from NetworkManager one year back due to constant issues with connecting to enterprise Wi-Fi with logs and errors that were difficult to debug or fix. It was also difficult to see where the failures occurred prompted me to move towards a more modular system.

The hacked system did not have a manager on top and it was cobbled together with:

1. wpa_supplicant for wireless.
2. dhcpcd for DHCP (wired and wireless).
3. dnscrypt-proxy for DNS over HTTPS and as a local cache.

Last week I started having problems when dhcpcd was not setting the proper network gateway and I couldn’t figure out what exactly was the issue since there were no updates to any of the affected programs. I realized that decoupling DHCP caused issues that can only be solved with a program that can react to network link changes properly. To be honest, this system did not have any issues for a long time and I could’ve just continued to use it after figuring out the problem but I thought it was time to try networkd.

systemd-networkd

It works similarly to how Systemd handles services. networkd uses INI style “.network” configuration files. Look at the man page for systemd.network for more information.

My motivation was to seamlessly handle wired and wireless interfaces without dropping connection due to state changes. For this purpose I had two files, /etc/systemd/network/20-wired.network

[Match]
Name=eno1

[Network]
DHCP=yes

[DHCP]
RouteMetric=10

and /etc/systemd/network/25-wireless.network with

[Match]
Name=wlp2s0b1

[Network]
DHCP=yes

[DHCP]
RouteMetric=20

You should start systemd-networkd.service and it should work with your existing wpa_supplicant@wlp2s0b1.service which should be setup separately. Network interface names eno1 and wlp2s0b1 are predictable and persistent across reboots, and are setup by Systemd.

My DHCP issue was solved by networkd knowing about both networks and handling them properly. The other nice property is I can set route metrics in the configuration which puts the kernel in charge of using the appropriate route when there are multiple gateways. Example of ip route with both interfaces connected:

$ ip ro
default via 192.168.1.1 dev eno1 proto dhcp src 192.168.1.125 metric 10
default via 10.46.255.254 dev wlp2s0b1 proto dhcp src 10.46.140.105 metric 20
10.46.128.0/17 dev wlp2s0b1 proto kernel scope link src 10.46.140.105
10.46.255.254 dev wlp2s0b1 proto dhcp scope link src 10.46.140.105 metric 20
192.168.1.0/24 dev eno1 proto kernel scope link src 192.168.1.125
192.168.1.1 dev eno1 proto dhcp scope link src 192.168.1.125 metric 10

Handling DNS

Systemd also comes with resolved which has a bunch of nice features and also integrates with options in the network files. However tempting this might be I still wanted to stick with my working dnscrypt-proxy setup. This is easily done by asking resolved to use 127.0.0.1 as its DNS server in /etc/systemd/resolved.conf. Now resolv.conf should have use 127.0.0.53 which is the resolved stub and it delegates the actual work to dnscrypt-proxy.

While you may feel, this is similar to NetworkManager I would point out that wpa_supplicant is handled separately and hence affords more ways to test your wireless connection before getting caught in an endless loop. Although if NetworkManager works for you, there isn’t a compelling reason to leave it. In the end, this was pretty easy to set up and the system looks more robust now.