Registration at Deutsche Telekom (CompanyFlex) has failed.... is not reachable, DNS error resolving FQDN, or service is not available.

[jacks]

Hello,

I’m new to 3cx and I have installed my first 3cx telephone system. We are using Deutsche Telekom Company Flex as siptrunk. It’s not working very well until now and I’m not sure, what I’m making wrong. Before we have used a Bintec be.IP Router as Mediagateway with the sip trunk and an old classic telephone system. It worked very well untel the old telephone system got broken

Now the most time the System is working well, but sometimes a day it happens, that the trunk is getting unregistered. In the eventlog I can find the following entry:

Registration at Deutsche Telekom (CompanyFlex) has failed. Destination (sip:217.0.XX.XX:5060;transport=TCP;lr) is not reachable, DNS error resolving FQDN, or service is not available.

And some seconds before:

Trunk L:10000(Deutsche Telekom (CompanyFlex)) has changed status to unregistered. This means that no more calls will pass via this trunk. Please check your network connection and the voip provider or other SIP PBX

As DNS Server I have configured 8.8.8.8.

I have also followed mostly the instructions under https://www.3cx.com/docs/deutsche-telekom-companyflex-sip-trunk/. But I didn’t configure inbound Ports, because we don’t have any phones or apps that are connecting from outside.

When the sip trunk is unregistered I have also tried to resolve the srv-Record on command line, what worked also without problems. I’m using the latest update.

Does anyone has an idea what could be wrong or are there further possibilities for debugging the problem in more detail?

Thanks and best regards from Germany

Jack

 

[leejor]

I'm assuming that the IP you X'd out is that of your provider. that being the case,it would not appear to be a DNS issue as 3CX has resolved to the correct destination. This suggests that your provider is not responding, for some reason. As this is intermittent, it make it much more difficult to troubleshoot, than somethimg that fails, all the time.

I would first see if there is any sort of pattern to this happening, time of day, perhaps? Record the times, for a few days and contact your provider to see if they can be of any help, based on when it is happening. Perhaps they have an intermittent congestion issue.

I have seen similar, intermittent logs (emails), with my own provider, where the trunk is not registered for a minute or two.

 

[jacks]

Hi,

thanks for your answer. I can’t see any patterns. Sometimes it happens in the night, sometimes in the day - regularly for 2 or 3 minutes. Sometimes it is alternating (registered / not registered) for minutes.

Because of the bad working fax-function, yesterday I have splitted out some numbers for fax from the trunk to a separate trunk. Now I have two trunks – one with numbers for speech and one with a few numbers for fax. I have registered the newly created trunk on a Fritz Box in the same network which is responsible for fax.

Today we had again some connection issues with the Deutsche Telekom trunk on the 3cx, but at same time the trunk, which is registered on the FritzBox, was not affected.

Are there any further log files, which are telling me the reason for the unregistered trunk? “DNS error” or “service not available” can stay for multiple issues. If not, the last possibility is to record some pcaps and analyze them….

Thanks

Jack

I'm assuming that the IP you X'd out is that of your provider. that being the case,it would not appear to be a DNS issue as 3CX has resolved to the correct destination. This suggests that your provider is not responding, for some reason. As this is intermittent, it make it much more difficult to troubleshoot, than somethimg that fails, all the time.

I would first see if there is any sort of pattern to this happening, time of day, perhaps? Record the times, for a few days and contact your provider to see if they can be of any help, based on when it is happening. Perhaps they have an intermittent congestion issue.

I have seen similar, intermittent logs (emails), with my own provider, where the trunk is not registered for a minute or two.

 

[YiannisH_3CX]

Hi @jacks,

Can you please tell me what PBX version you are running and if you have a static IP set in your PBX or dynamic?

From your description it seems to be a network issue so you will need to run some packet captures to determine if that is the case.
The TCP connection might be getting reset or the PBX is not receiving a reply to the register requests

 

[jacks]

Good morning Yiannis,

thank you for your answer. I have recorded some pcaps and could find retransmissions of tcp-pakets in the time the disconnection occurred. I have changed yesterday the interface from E100E to VMXNET 3 and have installed the openvm tools. Until now I can’t see any problems. But I’m not sure if this has been the reason. I have also updated the bintec router to the last firmware.

I’m using the latest release (18.0 Update 3, build 461).

The PBX is multihomed. One interface is located in a DMZ (which is directly connected to the bintec router and is also the default gateway). The other connection is located in the office-LAN and is responsible for connecting sip-phones and the 3cx-app to the PBX. Alle NICs have static IPs.

I will monitor the connection state for the next days and will get back to you with the actual state.

Thanks

Jack