Forward (redirect/nat) traffic with iptables

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Revision as of 15:01, 11 April 2013 by 217.30.203.164 (talk)
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If you want to redirect all traffic to IP 1.1.1.1 to IP 2.2.2.2, it simply can be done with iptables.
First of all enable IP forwarding in /etc/sysctl.conf on 1.1.1.1 host:

net.ipv4.ip_forward=1

Execute following for the changes to take effect:

sysctl -p

Now add the rules to related sections:

-A FORWARD -d 2.2.2.2 -i eth0 -p tcp -m tcp --dport 23:65500 -j ACCEPT
-A FORWARD -d 2.2.2.2 -i eth0 -p udp -m udp --dport 23:65500 -j ACCEPT
-A PREROUTING -d 1.1.1.1 -p tcp -m tcp --dport 23:65500 -j DNAT --to-destination 2.2.2.2
-A PREROUTING -d 1.1.1.1 -p udp -m udp --dport 23:65500 -j DNAT --to-destination 2.2.2.2
-A POSTROUTING -o eth0 -j MASQUERADE

Restart iptables

service iptables restart

Here is an example of working iptables:

# Generated by iptables-save v1.4.7 on Tue Apr  9 14:27:04 2013
*filter
:FORWARD ACCEPT [0:0]
-A FORWARD -d 2.2.2.2 -i eth0 -p tcp -m tcp --dport 23:65500 -j ACCEPT
-A FORWARD -d 2.2.2.2 -i eth0 -p udp -m udp --dport 23:65500 -j ACCEPT
COMMIT
# Completed on Tue Apr  9 14:27:04 2013
# Generated by iptables-save v1.4.7 on Tue Apr  9 14:27:04 2013
*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A PREROUTING -d 1.1.1.1 -p tcp -m tcp --dport 23:65500 -j DNAT --to-destination 2.2.2.2
-A PREROUTING -d 1.1.1.1 -p udp -m udp --dport 23:65500 -j DNAT --to-destination 2.2.2.2
-A POSTROUTING -o eth0 -j MASQUERADE
COMMIT
# Completed on Tue Apr  9 14:27:04 2013

Make sure your ssh port is out of range 23:65500, otherwise you will lose ssh access to 1.1.1.1