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I am using 3 ethernet interfaces on Ubuntu but when I restart, the default gateway is changing to a different interface. Each time I boot I have to change default gateway back to the eth1 by deleting the default gateway and adding it back with eth1. How can I fix this problem?

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Have you configured it manually using the /etc/network/interfaces file, or a with software like Network Manager or wicd? – Lekensteyn Mar 23 '11 at 12:56
"Gateway" is not equal to "route". A gateway is specific to an interface where an route says which interface should be used. – Lekensteyn Jun 2 '11 at 19:24
The gateway is usually an interface on a remote device which the local node is relying on for routing decisions. A route statement itself can refer to a local interface or not, but the routing destination has to be discoverable from a recursive lookup, connected interface, or default route. A default route or default gateway is the 'gateway of last resort' -- which will be used in the absence of a more specific route being available. – belacqua Oct 29 '11 at 22:14
Can you provide your routing table and list of interface, and other any relevant network configuration you've done? – belacqua Oct 29 '11 at 22:17
up vote 5 down vote accepted

Open the file /etc/network/interfaces

find desired interface and add following:

gateway 192.x.x.x

Restart network:

sudo /etc/init.d/networking restart
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What if the desired interface is configured via DHCP and I don't know the gateway address it will assign? – Aug 31 '12 at 10:40

To temporarily change the default route you can use an ip command like this:

$ sudo ip route change default via dev eth0

If you have a static ip configuration in /etc/network/interfaces you can add a gateway statement to make this permanent.

iface eth0 inet static

Using DHCP to configure networking you have to adjust another file instead. Add the supersede statement in /etc/dhcp/dhclient.conf.

supersede routers;
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