Registration has Failed, DNS error resolving FQDN but it is pingable

[SanderVV]

Hello

We have at least 20 3CX (debian) installs with the same provider without any problems. But 2 of these 3CX installs (on premise) have registration problems from time to time.

Warning in Event log is: Registration at TeleVoIP has failed. Destination (sip:XXXXXX;transport=TLS;lr;maddr=XXXXX) is not reachable, DNS error resolving FQDN, or service is not available.

At the same time we get this error and the registration failed, we ping (from the debian) to the same fqdn and it resolves without any problem and we get a respons. All other devices on the same network can also ping the fqdn of the sip trunk.

What else can I check to find the mistake?

 

[SteveITS]

Have you talked to the provider? Maybe they've blocked that IP from connecting for some reason. ("or service is not available") Does it recover by itself, and after how long?

 

[SanderVV]

Hey Steve

Thank you for the fast answer!

We have talked to the provider but they are not blocking the ip nor do they see any problems.

It does recover by itself but the time to recover is rather random.

some extra info: The connection to the provider is via TLS (with certificate) but its the same for all our setups that never have a problem with registration.

 

[YiannisH_3CX]

Warning in Event log is: Registration at TeleVoIP has failed. Destination (sip:XXXXXX;transport=TLS;lr;maddr=XXXXX) is not reachable, DNS error resolving FQDN, or service is not available.

The error you are seeing is generic and could be generated for a number of reasons. I don't think the issue is related with DNS resolution since the trunk is initially up and running. Once a registration is established 3CX will not perform another DNS query unless there is an issue with calls or registration.
Since its TLS a packet capture will not show much unless the connection gets reset from somewhere so you need to start from the basics.

What PBX version are running?
Does the firewall checker test pass?
How often does the issue occur?

We have talked to the provider but they are not blocking the ip nor do they see any problems.

The registration obviously drops at times so they should be able to at least see that and tell you what is causing this! Ask them what is causing the disconnect and from where it originates.