Port forwarding.

[Jaysnp101]

I must admit apart from @TimCurtis  there isn't many people on here that are willing to help over such a simple issue.

Anyway I found this:

https://community.bt.com/t5/Archive-Staging/Why-is-my-Hub-Default-Gateway-a-PRIVATE-IP-address/td-p/...

Is it possible im being double NAT'd as I also have a default gateway of : 172.16.xxx.xxx

When my public ip is: 86.136.xxx.xxx

Does this mean my public ip isn't really that public after all? 

[licquorice]

No, you are not double natted, the 172 address is the  address of the BT BRAS. Your gateway address is the next device to connect to and will never be your own public IP address.

As I said previously, are you sure your application is running and listening on the ports when you are testing to see if they are open. Ports aren't open continuously, they are opened by the application when expecting an incoming connection.

[Jaysnp101]

Thanks @licquorice  for getting back to me.

I'm certain the application is running and listening. I have tested other devices in the DMZ to check if the ports will open and they don't. Something is wrong on BT's end here and ill do whatever it takes to resolve it but its not acceptable. 

As far as I know they only reason DMZ wouldn't show ports open for several different devices and multiple checks would be because of double NAT. 

I'm obviously not the best at networking but I know enough to see something is wrong here.

[licquorice]

Well it isn't double Nat. I'm not in to gaming so can't help with the actual application and ports but as a test, I have a Raspberry Pi with a static IP address outside of the DHCP range of the hub and have installed an Apache web server on it and forwarded ports 80 and 443 and they work just fine. My gateway is also a 172 address.

Have you disabled UPnP, that should be disabled if you are manually forwarding ports to avoid any conflict.

[Jaysnp101]

Didn't BT test using CGNAT a few years back due to the lack of ipv4 addresses?

I honestly believe they have implemented something along the line which is causing these issues for so many people. Obviously 999 out of 1000 people would never notice due to not needing these extra bits like port forwarding so BT don't see it as a issue. 

Even with no port forwarding, no dmz , and no upnp ports 80 and 443 are open for me so maybe you should try testing other ports and see the results? 

[licquorice]

It is not CGNAT, there is a simple way to test for that.

Just go to whatsmyip and if it returns the same address as your hub shows to be your public IP there is no CGNAT.

Thousands of people use port forwarding succesfully, particularly to monitor CCTV cameras.

Unless you are running a web server and have forwarded those ports, 80 and 443 shouldn't be open.

[licquorice]

Just to humour you, I've started an  application to listen on port 50505. With the port forwarded (to a dynamic address) and the application running, the port is shown as open. As soon as I close the application with the port still forwarded, the port shows as closed.

[licquorice]

Have you tried a factory reset of the hub by pressing the recessed button with a pin for about 20 seconds until the lights flash? Remember to turn off smart setup again afterwards.

[Jaysnp101]

Ok, if I haven't got CGN then something else must be going on because my public IP matches that on the website.

I understand alot of people are using port forwarding and dmz but there's also alot of people who can't get it to work.

I've put the ps in the dmz, had the application running , checked the ports and still mostly closed except for the usual ones like 80 and 443 which are always open when I check. I have not got these ports set up for forwarding or anything but they still say open. 

I have factory reset the router from the router UI so I'm guessing the button on the back does exactly the same thing. I've done this on numerous occasions but it doesn't help. 

Thanks 

[Jaysnp101]

@licquorice I do have a ARLO security camera hub plugged into another ethernet port. These cameras use WiFi though so.they wouldn't cause any issues would they?