How to configure NAT to act as port restricted?

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QUESTION :

I am working on a project which require me to test with different type of NAT. I am using a laptop which is acting as Linux router. Due to some reason it is not able to correctly identify NAT with my stun server.

Here is section of code that I am using

iptables -t nat -A POSTROUTING -o $WAN -j SNAT --to-source 192.168.10.203
iptables -t nat -A PREROUTING  -i $WAN -j DNAT --to-destination 192.168.25.10
iptables -A INPUT -i $WAN   -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -i $WAN   -m state --state NEW -j DROP

Is there a better way?

ANSWER :

Do you mean that you want to configure PAT on your Linux software router?

If yes, please try to following command:

iptables -t nat -A PREROUTING -i eth0 -p tcp –dport 80 -j DNAT –to
172.31.0.23:80

This rule specifies that the NAT table use the built-in PREROUTING
chain to forward incoming HTTP requests exclusively to the listed
destination IP address of 172.31.0.23.

Here is a good guide about how to configure iptables.