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- Nov 17, 2017
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I have multiple instances of 3CX running all in different environments and different SIP Trunk providers all with what appears to be the same problem.
Outgoing calls will fail intermittently with the following error:
All instances running 3CX Pro 16.0.2.910
2 instances are Google Cloud Hosting deployed via 3CX PBX Express.
1 instance is on-prem Intel NUC Core i7 running Windows 10 Pro 1903
SIP Trunks are Skyetel (USA) and Breeze Connect (AUS) both are using the 3CX Certified Templates with no changes to their settings.
To me this looks like a DNS resolution problem. 0.0.0.0 is obviously not my SIP provider's IP address...
The host name for Skyetel is: transport-tcp.3cx.skyetel.com which doesn't resolve to anything...
So I checked with Skyetel engineers and they told me that host name was suggested by 3CX to force use of TCP (preferred by 3CX) instead of UDP for SIP connections (not RTP)
and 3CX looks for DNS SRV records for _sip._tcp.3cx.skyetel.com
and this returns:
Great! Except for there is still a problem given the failed outbound calls and the error above.
I have tried changing each instances DNS servers to Google 8.8.8.8 and 8.8.4.4 and CloudFlare 1.1.1.1 and 1.0.0.1
That did not fix the problem.
I have also tried creating a custom SIP Trunk and adding Skyetel's static IP addresses into the host name field. Then setting this custom SIP Trunk for outbound calls.
This does resolve the issue. However I want to know:
Why is the 3CX Certified template is not working?
How does 3CX specifically handle DNS resolution (SRV, A records, order of operations, etc.)
Outgoing calls will fail intermittently with the following error:
SIP Server/Call Manager ID: 12294
Call or Registration to 1800#######@(Ln.10000@Skyetel) has failed. 0.0.0.0 replied: 408 Request Timeout; internal
All instances running 3CX Pro 16.0.2.910
2 instances are Google Cloud Hosting deployed via 3CX PBX Express.
1 instance is on-prem Intel NUC Core i7 running Windows 10 Pro 1903
SIP Trunks are Skyetel (USA) and Breeze Connect (AUS) both are using the 3CX Certified Templates with no changes to their settings.
To me this looks like a DNS resolution problem. 0.0.0.0 is obviously not my SIP provider's IP address...
The host name for Skyetel is: transport-tcp.3cx.skyetel.com which doesn't resolve to anything...
So I checked with Skyetel engineers and they told me that host name was suggested by 3CX to force use of TCP (preferred by 3CX) instead of UDP for SIP connections (not RTP)
and 3CX looks for DNS SRV records for _sip._tcp.3cx.skyetel.com
and this returns:
Non-authoritative answer:
_sip._tcp.3cx.skyetel.com service = 20 50 5060 ca1.skyetel.com.
_sip._tcp.3cx.skyetel.com service = 10 50 5060 va1.skyetel.com.
_sip._tcp.3cx.skyetel.com service = 30 50 5060 or1.skyetel.com.
Great! Except for there is still a problem given the failed outbound calls and the error above.
I have tried changing each instances DNS servers to Google 8.8.8.8 and 8.8.4.4 and CloudFlare 1.1.1.1 and 1.0.0.1
That did not fix the problem.
I have also tried creating a custom SIP Trunk and adding Skyetel's static IP addresses into the host name field. Then setting this custom SIP Trunk for outbound calls.
This does resolve the issue. However I want to know:
Why is the 3CX Certified template is not working?
How does 3CX specifically handle DNS resolution (SRV, A records, order of operations, etc.)
