Question

26

Set specific interface for internet access

rated 0 times [ 26] [ 0] / answers: 1 / hits: 28721 / 2 Years ago, wed, may 11, 2022, 6:09:08

I have a machine with three network interfaces running Ubuntu 12.04 LTS, 64-bit, kernel 3.5.0-49.

I am using all three interfaces. Two of them are connected to LANs (eth0 and eth1) and one is connected to the internet (eth2); but when I try to access the internet, it attempts to go through eth0 (error responses come from eth0's IP).

I know that it will work (from experience elsewhere) if I don't set a gateway address for eth0 or eth1, but I have to because for some reason the network manager GUI won't let me save connection settings if no gateway is specified (?).

How do I either a) set eth0 and eth1 to not have gateway addresses, or b) tell the system to use eth2 for internet access (that is, IPs not on eth0/eth1's subnets).

As for trying to unset eth0 and eth1's gateway addresses: Trying to bypass the network manager GUI, I checked in /etc/network/interfaces but Ubuntu doesn't seem to use it (it only has an entry for lo). I'm not really familiar with more modern ways of configuring interfaces though, and so I gave up there.

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answered 2 Years ago ionodest · Accepted Answer

It sounds like you're looking for a way to set the default gateway. You can see the current settings by running ip route. You probably want yours to look like something like this:

default via 192.168.0.1 dev eth0 ...

192.168.0.0/24 dev eth0 ...

192.168.1.0/24 dev eth1 ...

192.168.2.0/24 dev eth2 ...

These routes are automatically created by NetworkManager. Try checking Edit ▸ IPv4 Settings ▸ Routes ▸ Use this connection only for resources on its network on the two LAN connections to prevent them from becoming the default gateway.

You shouldn't need to work around NetorkManager.