Solved SIP-Trun: DNS error resolving FQDN, or service is not available

[denko2k]

Hello.

We use a dynamic IP address (I know, that is is not supported by 3CX, but in the past it worked fine).
The IP address changes every 24 hours, at 23:55.

Since last night we have problems.
- DNS works fine
- pf sense DNS resolver cache was cleared
- windows DNS cache was cleared
- Services were restarted

We use 2 different SIP Trunks ("Deutsche Telefon Standard AG" sip.dtst.de and "Deutsche Telekom AG" sip.t-online.de). So there is no problem with the SIP trunk provider.

On every trunk we have this error:

SIP Server/Call Manager ID: 12293
Registration at DTST has failed. Destination (sip:[email protected]:5060) is not reachable, DNS error resolving FQDN, or service is not available.

STUN Server from 3cx are in use: stun.3cx.com, stun2.3cx.com, stun3.3cx.com
By the way: 3cx STUN servers do not respond on pings at the moment.

Can someone help?

 

[eddv123]

Hi Denko2k,

Dynamic IP addresses have been supported with 3CX since v15 (despite the fact they come up red in the management console interface).

What version of 3CX are you using currently - if not v15.5 (Latest SP) I recommend you upgrade.

To answer your question however I think it sounds like your NAT rule(s) could be worth looking at - with 3CX you need a full-cone NAT entry for Public to Private IP address.

 

[denko2k]

Hello. Thank you the your help. Indeed after a reboot of pfsense, the trunks worked fine. I will check my firewall config. I hope this still is up to date: https://www.3cx.com/docs/pfsense-firewall/

 

[denko2k]

Hello agian.
the problem has now been identified: the 3cx runs exclusively on a virtual windows server 2016. the windows firewall on this machine has been disabled because pfsense takes over this role. however, the last microsoft update has enabled the windows firewall. The consequence was that NAT (mapping) did not work properly anymore.

By the way:
What is the recommendation of 3CX? Should the Windows Firewall be disabled if a powerful firewall (pfsense, Cisco, etc.) is used?

 

[leejor]

did you have a read through...

https://www.3cx.com/docs/manual/firewall-router-configuration/

https://www.3cx.com/support/firewall-configuration/

 

[denko2k]

thank you. the issue is solved. the reason was the windows firewall.

 

[YiannisH_3CX]

Glad to see the has been resolves and thank you for updating the thread with your solution.