Forward (redirect/nat) traffic with iptables

From vpsget wiki
Revision as of 14:30, 13 June 2013 by Vq (talk | contribs)
Jump to: navigation, search

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.
You can also redirect traffic to specific port by specifying a port instead of range.

It's useful for example if you would like to configure "double openvpn": in this case you connect to 1st ip address which forward you to your open vpn server and you "exit under second ip".


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

add iptables rules

iptables -A FORWARD -d 2.2.2.2 -i eth0 -p tcp -m tcp --dport 1000:65500 -j ACCEPT #forward tcp port range
iptables -A FORWARD -d 2.2.2.2 -i eth0 -p udp -m udp --dport 1000:65500 -j ACCEPT #forward udp port range
iptables -t nat -A PREROUTING -d 1.1.1.1 -p tcp -m tcp --dport 1000:65500 -j DNAT --to-destination 2.2.2.2  #tcp port range
iptables -t nat -A PREROUTING -d 1.1.1.1 -p udp -m udp --dport 1000:65500 -j DNAT --to-destination 2.2.2.2  #udp port range
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Example for single port:

#iptables -A FORWARD -d 2.2.2.2 -i eth0 -p tcp -m tcp --dport 3389 -j ACCEPT #forward tcp port range

Save and restart

iptables-save >/etc/sysconfig/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

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