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This is my routing table when I connect my Android phone via USB to my Raspberry and enable USB-tethering.

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.42.129  0.0.0.0         UG    204    0        0 usb0
0.0.0.0         192.168.0.1     0.0.0.0         UG    303    0        0 wlan0
192.168.0.0     0.0.0.0         255.255.255.0   U     303    0        0 wlan0
192.168.42.0    0.0.0.0         255.255.255.0   U     204    0        0 usb0

I want wlan0 to be the preferred interface. So how can I change the metric of one the interfaces permanently?

Also how does Linux decide which metric value it will use for an interface?

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1 Answer 1

Reset to default
14

One of the solutions is to configure settings in /etc/network/interfaces adding default route with a predefined metric:

auto lo
iface lo inet loopback

# Primary interface
auto wlan0
iface wlan0 inet static 
    address 192.168.0.100
    netmask 255.255.255.0 
    dns-nameservers 192.168.0.1 8.8.8.8
    post-up /sbin/ip route add default via 192.168.0.1 dev wlan0 metric 10
    post-down /sbin/ip route del default via 192.168.0.1 dev wlan0 metric 10
    wpa-ssid <your_SSID>
    wpa-psk <your_PSK>

Maybe, you need to add another Wi-Fi options specific to your settings.

Another solution is to change the metric in the /etc/dhcpcd.conf. According to the dhcpcd manual metric can be assigned to the interface:

metric
         Metrics are used to prefer an interface over another one, lowest
         wins.  dhcpcd will supply a default metric of 200 +
         if_nametoindex(3).  An extra 100 will be added for wireless
         interfaces.

Add these lines to /etc/dhcpcd.conf:

interface wlan0
metric 200

interface usb0
metric 300

And restart dhcpcd and networking services.

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  • my /etc/networking/interfaces looks like this, so can I still add them?: # interfaces(5) file used by ifup(8) and ifdown(8) # Please note that this file is written to be used with dhcpcd # For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf' # Include files from /etc/network/interfaces.d: source-directory /etc/network/interfaces.d
    – MatMis
    Commented Dec 25, 2017 at 23:35
  • Could you please show the content of the directory /etc/network/interfaces.d? If there are no interfaces, you can add that config.
    – Gnat
    Commented Dec 25, 2017 at 23:40
  • 1
    /etc/network/interfaces.d is empty.
    – MatMis
    Commented Dec 25, 2017 at 23:44
  • I don't want to have a fixed default gateway and I still want to use dhcp. Do you know any other solution?
    – MatMis
    Commented Dec 25, 2017 at 23:56
  • Can you provide the output of the file /etc/dhcpcd.conf ?
    – Gnat
    Commented Dec 26, 2017 at 0:02

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