Linux Networking 101 : Connecting two machines through a Linux router.

We have the below scenario for connecting two machines via a router:

On the Linux router machine, we set up the two interfaces "eth0" and "eth1" as below.

First we enable the "eth1" interface:

Then we assign an IP address to it:

We also set up the "eth0" interface in the same way:

And we assign an IP address to it:

We then connect the interface "eth0" of the Host B to the "eth1" interface of the Linux router.

Configuration of Host B interface:

We enable the "eth0" interface of the Host B as below:

Then we give it an IP address:

We then add a default route on Host B, so the packet on Host B would know where to "go" when they leave the local subnet:

Enable routing on Linux router:

To enable our Linux router machine to act as a router, we need to set up the IP forwarding as shown in the below command:

Then we run the below command so that the changes would persist after booting the machine:

Configuration of the interface on Host A:

We start by enabling the interface "eth0":

Then we give it an IP address:

We then add a default route on Host A using the below command:

Remark:

The default route is used, when no specific route is set for a given IP address destination.

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