Linux Networking Cookbook

6.2. Setting a Default Gateway

Problem

You're a bit confused on the concepts of gateways and default gateways. When do you need them? What are they for? How do you configure them?

Solution

Gateways forward traffic between different networks, like different subnets, or your local network and the Internet. Another way to think of them is next hop routers. The default gateway contains the default route out of your network. Any host that is allowed access outside of the local network needs a default gateway.

Suppose your network is set up like this:

• Your LAN is on 10.10.0.0/24

• You have a single shared Internet connection with a static WAN address of 208.201.239.36

• Your ISP has assigned you a default gateway of 208.201.239.1

You'll need to configure two gateways: from your individual LAN hosts to your router, and then from your router to your ISP. Figure 6-1 illustrates this network configuration.

There are several different ways of configuring gateways on your LAN hosts. One way is with route:

	# route add default gw 10.10.0.25

Another way is with iproute2:

	# ip route add default via 10.10.0.25

Figure 6-1. LAN, router, and ISP gateway

If your PC has more than one network interface, you can specify a single one:

	# route add default gw 10.10.0.25 eth2
	# ip route add default via 10.10.0.25 dev eth2

But, these will not survive a reboot. Debian users have /etc/network/interfaces for permanent network configurations. ...