If you use NetworkManager with more than one interface, you probably want to control the metric of their routes. Here’s one way you can do it.
Background
I got a PCI Express WiFi card (wlan0) and a USB WiFi dongle (wlan1). On my system, NetworkManager will activate both at the same time. Then it gives metric 600 to the first one to be activated, and 601 to the second one.
What I wanted was to say: hey, NetworkManager, use metric 500 for wlan1 and 600 for wlan0. It doesn’t look like this is supported, though. Also, DuckDuckGo and Google didn’t help me much.
Digging through the nm-settings(5) man page, though, I found the route-metric option. It’s not ideal because it’s applied to a connection, not to a device. But it works fine for my use case as each WiFi interface is connected to a different WiFi network.
Step 1: Find out which are your connections
Use the nmcli helper to list your connections:
$ nmcli connection NAME UUID TYPE DEVICE Network 1 f0ed603c-f3c3-4acb-b54b-bb857bd9c5b5 802-11-wireless wlan0 Network 2 2b4b7240-36bd-407a-a3aa-169abb0ce6c4 802-11-wireless wlan1
As you can see here, each interface is using a different connection.
Step 2: Set the connection’s default route metric
For example, to set the wlan1 interface’s default route metric to 500, just change its connection:
$ nmcli connection modify uuid 2b4b7240-36bd-407a-a3aa-169abb0ce6c4 ipv4.route-metric 500 $ nmcli connection modify uuid 2b4b7240-36bd-407a-a3aa-169abb0ce6c4 ipv6.route-metric 500 $ nmcli connection show uuid 2b4b7240-36bd-407a-a3aa-169abb0ce6c4 | grep route-metric ipv4.route-metric: 500 ipv6.route-metric: 500
Step 3: Check that your routing table is correct
NetworkManager should automatically change the route’s metric:
$ ip route default via 192.168.25.1 dev wlan1 proto static metric 500 default via 192.168.0.1 dev wlan0 proto static metric 600 192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.111 metric 600 192.168.25.0/24 dev wlan1 proto kernel scope link src 192.168.25.69 metric 500
If it didn’t, try restarting NetworkManager.
Nice summary & good (if hidden) tip!
In one of my use cases, on a Raspberry Pi 2 running a Debian (jessie) based distro on armhf architecture, NetworkManager 0.9.10.0-7 does not offer the route-metrics option. So YMMV if using older NM versions.
Thanks again,
Adam.
Thanks from me, too. This lets me setup my network routing rules the way I really need them much easier 🙂
How can I make these changes persistent? Do you have an example boot script or systemd service?
The changes are persistent. They get applied to the applicable connection profile in /etc/NetworkManager/system-connections/
This has been irritating me for months: My lab network connection was always getting a lower routing metric than the corporate connection, so my ritual on every logon has been disconnecting the two connections and then reconnecting them in the order I want them in. Now I can concentrate on drinking my coffee. Thanks!