Extension no longer registering

[Napocensis]

Hello,

I have a Grandstream GXP2135, which has two extensions. Both stopped working today, and the same happened with one extension on a Yealink SIP-T42G.
Restarting the Yealink re-registered the extension.
Restarting the Grandstream re-registered only one of the extensions.
I restarted all services on the 3CX V15.5 and it did not fix the problem. I then restarted the Windows server, but to no avail.
To note that other Grandstream phones maintained service throughout, and there were no changes made to the phones or the 3CX server.

Any idea how I can re-register that one extension other than re-creating it, and what is causing the issue?

Thank you.

 

[leejor]

Are these local, or remote sets? Relatively new installation? Any changes to anything?

 

[Napocensis]

They are all remote extensions, connecting to a cloud machine. Neither the 3CX, nor the phones have had any changes in months. Automatic updates are turned off across the board.

 

[leejor]

Are you using STUN, VPN or an SBC to connect?

 

[Napocensis]

I am using STUN.
The second extension on the same phone connects and functions normally, which is very strange, as STUN settings appear to be at phone level, not extension level...

 

[leejor]

Did you check the 3Cx Activity Log to see if there are registration attempts from the other sets? How long has this been working (I assume correctly)?
Were each of the sets assigned unique local port numbers initially?

 

[YiannisH_3CX]

If the phones are using the same sip port then it could cause a conflict that could cause the extension to un-register. As mentioned make sure that each device uses a unique SIP port and unique RTP ports to avoid any issues and make sure that those ports are forwarded to the local IP of the phone.
https://www.3cx.com/3cxacademy/videos/intermediate/configuring-remote-extensions/