IP phones suddenly not showing as online on V20 3CX

[BKSupport]

Hi all, apologies if this isn't as details as I can express.
I've had 3CX working quite smoothly the whole of last week but this morning, it looks like my 3CX has suddenly dropped all the IP phones.
Mainly the reception phone that has a sip trunk. - It's showing up as RED and offline, I don't believe anything has changed and I've restarted the VM responsible for handling 3cx.

What could have gone wrong?

Any help would be appreciated!

Thanks!

 

[JohnS_3CX]

Some common reasons:

1. Your 3CX IP has changed and the phones don't know how to reach it.

2. Or the phones were not correctly configured (ie. if they were added as Local, but they are actually remote).

 

[BKSupport]

Hey John, thanks for the rapid reply.
I can see that my 3CX IP has remained the same.
In regards to the configuration of the phones, it does show up as a local phone but that's actually cause they are local?
In the same building I am in.

I would also like to add that they were showing online fine for the last 5 days and it's just now that they're failing to show online and unprovisionable.

Do you have any more information?

Thanks!

 

[JohnS_3CX]

By Local we mean same LAN and IP range as 3CX, not separated by subnets or VLANs that can't reach each other.

This is normally the case, but sometimes people have different networking arrangements which prevents them from reaching 3CX even if they are local (ie. segregated local networks or VLANs)

But keep in mind that V20 requires Split DNS, so that local phones will be given the local IP of 3CX which is internally reachable for them. Make sure you do indeed have this https://www.3cx.com/blog/releases/split-dns-on-prem/

It would seem like a networking issue at first glance.

 

[BKSupport]

Oh sure, they are most definitely local.
Since they all share the same VLAN - 250
Here are the following details

3cx - 10.3.250.10
Mainphone - 10.3.250.101