This quick tutorial will show you how to set which network Linux uses to access internet when multiple networks are connected by setting the default route.
If you have a Linux device (for example a Raspberry Pi) connected to multiple networks (like being connected to a wireless and wired network simultaneously), you might have trouble connecting to the internet.
That’s because Linux will have automatically set up some default routes, and will have somewhat arbitrarily picked which interface it tries to use to access the internet – even if there’s no internet available on that interface.
Forcing Linux/Raspberry Pi to Connect to the Internet via a Specific Network
Follow these steps to update your default route to use the correct network.
List Current Routes
You’ll need to know what the current routes are to issue the commands to modify them. Run:
netstat -rn
You’ll see something like the following:
Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth0 10.10.10.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
In the example above, the network address 192.168.0.1 is the default route – the route Linux uses for any route which isn’t matched elsewhere in the routing table. It’s associated with the network on eth0 – the wired ethernet connection.
However, in our scenario the network on the second listed connection, wlan0, is where the internet router actually is. The default route must be altered to reflect this.
Issue the following commands to change the default route, replacing 192.168.0.1 and 10.10.10.1 with the IP addresses you are using on your network.
ip route del default via 192.168.0.1 dev eth0 ip route add default via 10.10.10.1 dev wlan0
In the first command, the default route is identified by the IP address and interface and then deleted.
In the second command, a new default route is defined, specifying the correct router IP address and network interface.
