Yealink Phones not showing the correct IP in 3cx

[Sully]

Good Morning!

Ran into this yesterday with a working 3cx version 18 Self Hosted in Azure, local sbc onsite. Environment has been great for 2 years and all of a sudden the phones were not showing their correct IP in 3cx. The phones are 2.x on a voice vlan. I noticed when I restarted the phones or network, the sbc would pick them up briefly as "New" Phones and it would actually show the correct IP with a 2.x. After a short time, they would register to correct users, but the ip would change to the local firewall IP with a port. Example: "192.168.1.1:65480: via SBC" The other phones would have a different port. This all feels like a potential SBC issue but it also feels networking related but nothing has changed on the network. If I log into the switch & firewall the phones show correct with 2.x. Thanks for any thoughts!

 

[JohnS_3CX]

Hi Sully,

Sounds like your firewall is rewriting IPs.

What are you using as an SBC, and does it have only a single NIC as it should?

 

[Sully]

Hey John,

The SBC is working on a local windows server with a single NIC. It was just weird that the SBC initially showed the correct IP's. I believe everything is working ok at the moment. I've just never seen this behavior.

 

[JohnS_3CX]

Well, 3CX is getting those IPs from somewhere, and if the phones actually have the correct IPs then something is definitely up.
It could potentially also lead to some problems with audio, so keep an eye out for that kind of issue.

Can you confirm that the SBC is actually on the same subnet and IP range as the phones?
1. They are not meant to exist on different VLANs - they must be together on the same one.
2. And the IP addresses must be RFC1918 range compliant.

 

[Sully]

Thanks! You confirmed what our next steps are going to be regarding the sbc on the same VLAN.