PORTFORWARD CHECKER SOFTWARE
If loopback failed then you likely have either a software firewall on the host, or a hardware firewall or NAT router between the router and the host.
PORTFORWARD CHECKER PC
make sure that the PC is running the program that you're trying to forward the port for so that it will accept the connections. Make sure that the host that you're forwarding to is listening on the port being forwarded to.If you disabled the SPI firewall then you will have to enable it temporarily to be able to change this setting. Uncheck Filter WAN NAT Redirection (it is by default) which means loopback will be allowed.
![portforward checker portforward checker](https://i.pcmag.com/imagery/articles/07o2jA2YnPUmtQoaT73HcOo-1..1577582453.jpg)
Go to the Security -> Firewall page in the GUI.To test a single TCP and UDP port number with Nmap, use the following options: If you don't have an obvious client program capable of this (like a web browser to connect to a HTTP server) then you can use Nmap to check if the port is open. This test will only work if you're using a client program that allows you to specify the IP and port to connect to. Some ISP's block certain ports or even do deep packet inspection (OSI layer 7) so to determine if the port forward is working you should try to access it from within your LAN using NAT loopback. Any other WAN IP is likely a public (routable) address that just needs a properly configured port forward on the router.You must configure that router to either DMZ or port forward to the DD-WRT router. If the WAN IP begins with .x, 172.x.x, or 10.x.x.x then the router is behind another router that is also doing NAT.If it's the latter then you need to fix your internet connection which is a different matter not discussed here. If it's the former then no port forwards are needed on this router because the device is not doing NAT or routing. If the WAN IP is 0.0.0.0 then you're using the device in an OSI layer 2 bridge/switch configuration (WAP, WDS, CB, RB) or you have no internet connection.Start by going to the router's GUI with your web browser and checking what the router's WAN IP is. If you have a lot of changes then you'll likely want to test other possibilities first since most problems are user error anyways. If you have made few changes from the default configuration then you should try this first. The only cases I've seen of genuine bugs with port forwards in DD-WRT have been unexplainable behavior of the underlying iptables rules that was fixed by hard resetting and reconfiguring from scratch. Basic Troubleshooting Did You Hard Reset?
PORTFORWARD CHECKER HOW TO
You should first familiarize yourself with how to configure Port Forwarding before trying to troubleshoot it. There can be many problems including multiple layers of NAT (router behind another router), misconfiguration of the port forward, software firewalls on the host being forwarded to, unexplainable behavior caused by not hard resetting the router, etc.
![portforward checker portforward checker](https://eu.dlink.com/uk/en/-/media/faqs/uk/dir/3-dir-857-port-forwarding.png)
This page explains how to troubleshoot common port forwarding troubles to figure out what the problem really is so that you can fix it.