Port Forwarding and DMZ Function both don't work on the DG8041W-2.T5

[TemPary]

I'm trying to open a TeamSpeak server on my PC, which requires me to forward some ports to help make it work. I logged into the online router portal and forwarded the respective TCP and UDP ports, and checked using an online port checker which says that the ports are still closed.

To make sure, I just enabled the DMZ Function on my PC IP and every single port I check still comes up as closed.

Why is that? I've used the DMZ and port forwarding functions on other routers without further setting up on my PC and they've all worked fine. I just can't get this router to work and hence can't open a TeamSpeak server. 

Please help.

[Chris-TalkTalk]

Hi TemPary,

Glad to hear that, with Keith's help, you managed to resolve the problem 🙂

Chris

[KeithFrench]

Glad it is working, this server may not listen for the UDP until such times as the user is logged in.

[TemPary]

Thank you for the detailed explanation!

This time I made sure everything was set up by connecting to the TeamSpeak server using my mobile phone on mobile data, and it worked. Then I asked my friends to connect again, and it worked for them after a few tries too!

I don't get why they had to try multiple times but as long as they can connect, I guess my issue is resolved.

Thanks again for the help!

[KeithFrench]

The problem is that, unlike TCP, UDP is a connectionless protocol. This means that the sending end does not try & setup any session with UDP port 9987, it just sends the UDP packet to 9987 & quite frankly doesn't care if it gets there or not. It relies on upper-layer protocols to determine this. You have an application (whatever sort of server that you are using) which will react to UDP packets coming in on UDP port 9987, but crucially it does not open this port like TCP does. This is why port-checking websites only work with TCP.

What I do is disconnect a smart phone from Wi-Fi, so as it has to use mobile data. Then I send the UDP packet from an application on there out to the internet destined to either the router's WAN IP address or a DDNS domain. This resolves any issues with NAT loopback being blocked in the router. The application includes a text message that it puts in the UDP packet. At the incoming end, I use an application that I wrote myself that can read the contents of that UDP packet & display the text message in it. Alternatively, Wireshark can always be used to monitor traffic coming into the device running the server software, if the OS supports it. Check in the resulting trace for the UDP packet that contains the same text message.

Whether you can check yourself will depend on what sort of device your server is running on, its OS and your skill levels. The most likely cause of your problems is any firewalls on the device, is the UDP side of your server running & waiting for connections on this port, or its configuration? The router is not to blame.

[TemPary]

How are you sure that the UDP port is actually forwarded if you can't check using online tools? Just want to know so that I can confirm as well.

[KeithFrench]

I can now confirm that the router definitely forwards UDP port 9987 OK. This is the rule I used:-

UDP Port 9987 PF rule

[KeithFrench]

OK I have managed to get something to work from my Android, but I won't have a chance to test until tomorrow.

[KeithFrench]

I don't currently have any effective UDP client to work with, but if yours should work fine.

[KeithFrench]

UDP is not compatible with port checking websites, so will always show as closed.

[TemPary]

Ok so I realized that yes, the TCP port does indeed work when the server is running, but the UDP port doesn't. That's a shame because the UDP port is responsible for the actual voice chat in the server. Please get back to me on this whenever you figure out a fix. Thanks.

[KeithFrench]

The TCP one works perfectly, the UDP one needs a bit more inventive testing. I'll get back to you later on that. Have you allowed them both through any personnel firewalls on the device being forwarded to.

[Debbie-TalkTalk]

Thanks @KeithFrench 

[KeithFrench]

They shouldn't be a problem at all, let me test your rule on mine & I'll get back to you.

[TemPary]

This is one of the ports I need to forward. The other one is 9987 on UDP. I've turned off DMZ Function for now, by the way.

[KeithFrench]

True, there are some ports it does not forward. Please include a screenshot of at least one of the port rules that you are trying, so as I can check them for you. If there are other TCP or UDP ports, please let me know.