Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report

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Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report

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Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report
Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report
2022-04-28 17:37:14 - last edited 2022-06-23 10:11:31
Model: Archer C80  
Hardware Version: V1
Firmware Version: 1.10.0 Build 210716 Rel.51301n(5553)

Today while troubleshooting on WireGuard vpn port forwarding, I noticed a strange behavior. WireGuard VPN works on UDP default port 51820, and I have added it in port forwarding, and everything seems to be working fine, but later for testing purpose I disabled the port forwarding and tried to connect VPN from my mobile, and it still working. Technically it should stop working, but somehow it didn't disabled it. If I delete the entry, then only it is getting disabled.

 

How to reproduce this:

1. Create UDP port forwarding for WireGuard.

2. Try to connect to VPN from different network, it should start working.

3. Disconnect VPN form mobile.

4. Now, disable port forwarding.

5. Again try to connect to VPN from different network, and strangly it should start working.

6. Disconnect VPN form mobile.

7. Delete UDP port forwarding from router.

8. Try to connect to VPN from different network, this time it will not work.

 

I have tested this multiple times, and getting exact same result. I guess this a BUG.

 

Regards,

Saugata D.

 

 

Sometimes while trying to re-enable it, getting this error as well.

Regards, Saugata D.
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#1
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3 Reply
Re:Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report
2022-04-28 20:42:08

  @iAmSaugata 

 

Usually this error message: "Confliting with existing port." appears when the UPnP has opened a port, but you're trying to open the same port via Port Forwarding as well.

The router UPnP feature may interfere with the Port Forwarding if they are active at the same time.

Try disabling UPnP in NAT Forwarding menu and then make the same test to see if there's any difference.

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Re:Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report
2022-05-02 14:41:29

  @terziyski 

The error I got is not from uPNP, I have uploaded a video, please have a look.

 

https://youtu.be/RNYBxjLR9BE

 

Scenario:

UDP port 51820 enabled in NAT Port Forwarding.

Mobile is connected to WireGuard VPN from Mobile Data.

Now, if I disable the NAT Port Forwarding in router, it will not blocking the port for external connection, I can still able to disconnect and connect VPN from Mobile.

Even at this point, if I reboot router, after rebooting, I am still able to connect and use same UDP port, and now if i try to enable WireGuard UDP port in NAT Port Forwarding, I am getting conflict error.

 

I do not think this is expected behavior from router, at least not after rebooting the router itself. It looks like, during reboot it failed to disable the port as per settings. This should be investigated, as it could lead to some issue for well-known ports.

 

I am not sure if this is applicable for TCP ports as well, but I will be going to check.

Regards, Saugata D.
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Re:Strange behavior on UDP Port Forwarding - Archer C80 - Bug Report
2022-05-02 17:48:10

  @iAmSaugata 

 

Yes, it seems that this should be attended by TP-Link as the way it goes.

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