Centos – IP to IP forwarding with iptables [centos]

centosforwardingiptableslinux-networking

I have 2 servers. Server 1 with ip 1.1.1.1 and server 2 with ip 2.2.2.2

My domain example.com points to 1.1.1.1 at the moment, but very soon I'm going to switch to ip 2.2.2.2. I have already setup a low TTL for domain example.com, but some people will still hit the old ip a after I change the ip address of the domain.

Now both machines run centos 5.8 with iptables and nginx as a webserver.

I want to forward all traffic that still hits server 1.1.1.1 to 2.2.2.2 so there won't be any downtime.

Now I found this tutorial: http://www.debuntu.org/how-to-redirecting-network-traffic-a-new-ip-using-iptables but I cannot seem to get it working.

I have enabled ip forwarding: echo "1" > /proc/sys/net/ipv4/ip_forward

After that I ran these 2 commands:

/sbin/iptables -t nat -A PREROUTING -s 1.1.1.1 -p tcp --dport 80 -j DNAT --to-destination 2.2.2.2:80
/sbin/iptables -t nat -A POSTROUTING -j MASQUERADE

But when I load http://1.1.1.1 in my browser, I still get the pages hosted on 1.1.1.1 and not the content from 2.2.2.2. What am I doing wrong?

Best Answer

Try changing -s 1.1.1.1 to -d 1.1.1.1

You want to match the destination address and not the source address...

You also need to adjust your MASQUERADE-rule to include the interface the traffic takes on the way back. (Most likely eth0 or similar).

Do this with the -o flag. For example like this: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

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