Changing NetworkManager route metrics

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.