Should port forwarding work inside the LAN?

[dansmith21]

I'm troubleshooting a port forwarding issue, and just want to confirm how port forwarding is expected to work:

- I have a web server running on my laptop on port 2222 of my laptop, bound to all interfaces; the laptop's IP address 10.0.21.74

- My router (Nest Wifi) has LAN address 10.0.21.1

- Under "Port Management", I've configured port 2222 (TCP & UDP) to forward from 2222 on the router to 2222 on my laptop

If this is functioning properly, when I'm inside the LAN and connect to 'http://10.0.21.1:2222/index.html', should I expect the same result as 'http://10.0.21.74:2222/index.html'? That is, does port forwarding work with the LAN address? Or only the WAN address?

(Ultimately, I'd like to this to work from the WAN, but I'm troubleshooting and trying to figure out if it's the Nest Wifi or my ISP's modem that is to blame for my issues.)

[MichaelP · Accepted solution]

Hello @dansmith21 

So, a couple of things to be aware of here. First, the Nest WiFi firewall/router has two IP addresses: one for the inner network that it creates (10.0.21.1 for you, apparently), and another IP address for the external interface the rest of the world sees. That WAN IP address is the one that external hosts will connect to in order to get through your port mapping to your internal server. Testing directly against the router's internal IP address is unlikely to work.

Secondly, some (but not all) router/firewalls support "hairpin" or "NAT loopback" for testing. It looks like Google/Nest WiFi does not. This means testing against that external IP address won't work from inside your internal network. So, you'll need an external host to test it (e.g., a cell phone not connected to your WiFi).