NAT from Pvt ip to PublicIP

Question

I have a gateway machine with 2 NIC: eth0 with public IP and eth1 with private IP.

On eth0 I have 4 public IP aliased, I wanted to NAT public IP to private IP and I used DNAT to do that uisng iptables.

1.1.1.2 -> 10.10.10.2
1.1.1.3 -> 10.10.10.3
1.1.1.4 -> 10.10.10.4

Rules

-A PREROUTING -d 1.1.1.2 -p tcp -j DNAT --to-destination 10.10.10.2
-A PREROUTING -d 1.1.1.3 -p tcp -j DNAT --to-destination 10.10.10.3
-A PREROUTING -d 1.1.1.4 -p tcp -j DNAT --to-destination 10.10.10.4

and now I am able to reach internal IP with DNAT, but not able to connect with external network from this private IP.

How can I achieve that? Can SNAT be done for multiple IPS?

Answer 1

Seems to be that you forgot to add masquerade rule.

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

This is kind of SNAT. It replaces source LAN IP to router's external IP in packets, originating on LAN machines. Thus, external machines know whom to send the packets.

Answer 2

I guess it can be done. Just specify -s <int ip> and --to-source <ext ip>

iptables -t nat -A POSTROUTING -s 10.10.10.2 -i eth1 -j SNAT --to-source 1.1.1.2