Busy Tone But Extension online

[BCS-Tech2]

We have one customer that has 3 offices. One home office is where the on premise 3CX is hosted and to others are connected to the home office through site-to-site VPN. There are extensions in all the offices. The remote phones are connected using local LAN. The system has worked for 2 years without any issues.

On Wednesday of this week, we upgraded the internet service at one of the locations to a faster service and put in an a new firewall. Setup the VPN and everything back up and running. Everything looks good.

But one extension at the upgraded site is giving me some serious heartburn. The 2 older Cisco SPA525Gs phones at this site are working. But a Yealink T28S is having issues. The user can receive outside and inside calls. They pick the receiver up a make to a call and they hear the dial tone. But when they dial a outside number or an extension, they get a busy signal.

The call log shows
Authorization system can not identify source of: UnkSrc Recv Req SUBSCRIBE from 192.168.30.43:5060 tid=662133664 Call-ID=[email protected]:
and
From: "Front Desk" <sip:401@173.166.209.XXX:5060>;tag=662035726

The 173.166.209.XXX is the public IP of the new ISP service. No traffic should be hitting that ip address.

The other extensions work, why not this one. No SBC is installed, but might have to install one.

Any suggestions?
Thanks

 

[leejor]

My first guess would be an incorrect STUN setting. I assume that the sets should not be using STUN, because they are either locally hosted, or using VPN?

Since you've also changed the firewall, it might also be that.