Solved All of a sudden, 90% of our phones show "No Service"

[Frank86]

About 50 Yealink phones (T41, T42, T46, all with latest firmware and standard templates) all of a sudden show a "no service" message.
Both 3CX (latest version on Windows) and the network report no issues. 3CX is installed on the local network. Most of the phones that report "no service" are on the local LAN.
Nothing has changed on the network or in 3CX. The phones reported the problem at the same time.
Resetting the phones to factory settings and reassigning them to the extensions works (at least on the two of them we've done so far).
Never seen anything like this before. What could be the cause?

 

[SuperTima]

Frank, do you guys have SBC (session border controller) in the office LAN? If you do, have you tried restarting it and then restarting a couple of phones?
My understanding, just restarting (power-cycling) the phones does not make any difference - is that correct?

 

[cobaltit]

Frank, do you guys have SBC (session border controller) in the office LAN?

Since he mentioned that 3CX is installed on the local network and that most of the phones that report no service are on the local LAN I assume there is no SBC involved, or at least a SBC shouldn't be involved for local to local.

I'm curious what 3CX version he is on (latest version can mean different things depending on when someone reads this post and if you are running a beta. My guess would either be a blacklist entry or DNS issue.

 

[JohnS_3CX]

Hi Frank,

Sounds like a possible network issue or SIP server issue, but please start from here so we know what environment we are looking at: https://www.3cx.com/community/threads/information-to-provide-when-requesting-help.67558/

 

[Frank86]

No SBC involved as all the phones are on the local LAN.

I think the problem was related to issues with the 3CX server's second IP address. We inherited a server with two IP addresses, as the previous IT manager was moving all the phones from one VLAN to another but didn't get a chance to complete the project.

Once I reconfigured all the phones on the same VLAN and disabled the second IP on the 3CX server, all the phones came back up.

 

[JohnS_3CX]

Hi Frank,

Glad to hear all is well, sounds like you now have it under control