Most common SIP trunk configuration mistakes

This is a collection of the most common SIP trunk configuration mistakes that usually result in trunks not working or only working in one direction.

Missing context=from-trunk statement in trunk configuration
Also using context=some-custom-context which is also incorrect unless you have manually created some-custom-context in the dialplan.  The context from-trunk is already created for you by default in Freepbx dialplans.

Using host=somednsname.com when calls come in from multiple IP addresses  
If the IP does not match the resolved DNS name (done at the time trunk configuration changes are applied to the PBX) the call will fail.  If a SIP trunk provider sends calls from multiple IP addresses you need to create a separate trunk for each IP address so that you have host=xx.xx.xx.xx corresponding to each IP address.  This is done in PEER Details.  Only one trunk needs a registration string.  The registration string CAN use DNS since that goes the other direction to register your PBX IP address with the SIP provider.

The best clue that your SIP provider likely sends calls from multiple IP addresses is if you do nslookup somedomainname.com and it returns more than one IP address.  Those are the IP addresses you need to use instead of the DNS name.

Adding allow=g729 when no g729 codec or license is installed  See this related FAQ.

  • sip, trunk, configuration, troubleshoot, mistake

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