One-to-one NAT

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One-to-one NAT is a way to make systems behind a firewall and configured with private IP addresses (those addresses reserved for private use in RFC 1918) appear to have public IP addresses.¹

I'm using this type of setup, with three public IPs. WRT54GL v.1.1 with DD-WRT RC6 and it works just fine.²

I have done following:


Contents

Setup

Startup

set up new public static ip on dd-wrt wan interface vlan1

ifconfig vlan1:1 PUBLIC_IP netmask NETMASK broadcast BROADCAST 


Firewall

SNAT/DNAT

route all packets for the new public ip, to a certain local ip

iptables -t nat -I PREROUTING -i vlan1 -d PUBLIC_IP -j DNAT --to-destination LAN_IP

masquerade returned packets from the local ip to the public ip

iptables -t nat -I POSTROUTING -o vlan1 -s LAN_IP -j SNAT --to-source PUBLIC_IP
PORT FORWARD

forward port X to above local IP

iptables -I FORWARD -p tcp -i vlan1 -d LAN_IP --dport X -j ACCEPT

You could also replace above rule with the following:

iptables -I FORWARD -p all -i vlan1 -d LAN_IP -j ACCEPT 

which instead of forwarding just a single port, will let through all tcp/udp connections on all ports to this public ip-->lan ip.

With other words, no firewalling what so ever.

Resources

¹ http://www.shorewall.net/NAT.htm
² http://www.dd-wrt.com/phpBB2/viewtopic.php?t=24555