Two Network cards and ip forwarding

Question

I want to make "Ubuntu 11.10" act as a router.

I have two LAN interfaces.

Let's say interface A' IP is 172.16.1.10 ;
interface B's IP is 192.168.1.10.

How can I configure Ubuntu so that 172.16.1.1 can connect to 192.168.1.1?

Answer 1

Sounds as if you are configuring a router.

You only need to make a few changes to enable IP forwarding

Enable IP forwarding

echo 1 > /proc/sys/net/ipv4/ip_forward

Configure iptables

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

See also Ubuntu Wiki router

You will likely want to learn a little about iptables

Linux Firewalls Using IPTables

If all that seems a bit overwhelming, may I suggest you consider one of the linux distributions that are built to act as a router ? I like smoothwall, but there are others to choose from.

smoothwall

Firewall specific distros will handle most or all of the configuration for you and most come with a web based interface to make it ever easier.