Às vezes é chamado de Port Address Translation (PAT) ou Network and Port Translation (NAPT)
Não é mencionado na documentação do DD-WRT Encaminhamento de porta
No entanto, ele discute "Port Mapping"
Example: To map port 81 to internal port 80 on 192.168.1.2 issue the command
iptables -t nat -I PREROUTING -p tcp --dport 81 -j DNAT --to 192.168.1.2:80
iptables -I FORWARD -p tcp -d 192.168.1.2 --dport 80 -j ACCEPT
The down side with this is that it's not as obvious as the other methods but you can use a program called Firewall Builder to make this simpler. This setting will also disappear on router reboot if you don't place these commands inside of a Startup Script.