Creating a router on a CentOS 6 server

Assuming you want to NAT the network on eth1 and route the traffic to eth0 this is the spell:

Create the forwarding rule:

/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

and then enable IP forwarding

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

OR

sysctl -w net.ipv4.ip_forward=1

 

Permanent setting using /etc/sysctl.conf

If we want to make this configuration permanent the best way to do it is using the file/etc/sysctl.conf where we can add a line containing net.ipv4.ip_forward = 1

/etc/sysctl.conf: net.ipv4.ip_forward = 1

if you already have an entry net.ipv4.ip_forward with the value 0 you can change that 1.

To enable the changes made in sysctl.conf you will need to run the command:

sysctl -p /etc/sysctl.conf

On RedHat based systems this is also enabled when restarting the network service:

service network restart

 

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