Phone provisioning issue

[LPG]

Hi. I was wondering if there is a document available which shows the steps a phone takes to provision so I can troubleshoot better.

3CX v18 Self cloud hosted with Linux SBC. Grandstream GRP2613 phones.

When setting up in lab environment, the SBC and phone are in the same LAN, the phone provisions perfectly and immediately.
As soon as I take the SBC and phone to the customers site, the SBC re-registers to the 3CX server with its new IP, the phone (an unprovisioned GRP2613) boots and displays as a new phone in 3CX phone section as normal, but when assigning it to an extension, it never starts provisioning. I have noticed that the DNS server for this client is not the local dns of the router, but to a DNS server over a VPN to their software provider, so it could be related to restrictions on their side. I will begin by making the DNS server on the phone and SBC point to the local router instead to the providers over the VPN. Does this sound just like a DNS issue or something else?

What happens when the server tries to push the provisioning to the phone through the SBC? Is there a DNS lookup needed that is failing, multicast, blocked port (even though it’s on the same LAN as well), DHCP option 66?

Any thoughts as to where to proceed outside of the DNS server change If that doesn’t work?

One of those hard things to troubleshoot when you enter into a network which was configured by a 3rd party!

Thanks for your help.

 

[JohnS_3CX]

The phone will need NTP (because TLS connections require it), and DNS (so it can find the 3CX server), and internet access to reach the 3CX server. If some of those are not met, it will sure try but it will fail.

What happens when the server tries to push the provisioning to the phone through the SBC?

We don't do that, the SBC just instructs the phone to go fetch its own provisioning straight from the PBX URL. Hence the above requirements I mentioned.

Option 66 won't help you either, it only does the part where it gives the phone a URL.

It's not an easy task for sure when you don't manage the network, but you could start a pcap on the phone, then provision it via SBC. Give it a minute, then end the pcap.

You will see

1. The SBC IP sending the phone a SIP NOTIFY with the URL
2. The phone will try to resolve the URL (does it resolve to 3CX?)
3. If it resolves, it will also try to hit up your NTP and sync time so it can connect via TLS to 3CX (does it manage to get through?)
4. If it gets this far, it will attempt to download its config and provision itself.

You will probably find a failure in step 2 or 3