This troubleshooting guide demonstrates the options available when a configured SIP line cannot register with the provider.
If the DNS settings are not configured correctly in your LANCOM router, the router will not be able to correctly resolve the DNS address of the SIP registrar (e.g. tel.t-online.de).
In this case you should check the DNS settings of your LANCOM router in the menu IPv4 → DNS. If DNS requests are explicitly forwarded to specific remote sites, you should check that the Forwarding settings are configured correctly.
Information on how to configure DNS forwarding is available in this Knowledge Base document.
How you generate trace output with LANconfig
is described in this Knowledge Base document
2) Is the correct Internet connection being used for SIP line registration?
If you have configured multiple Internet connections and your VoIP line requires the use of an Internet connection belonging to the provider, you should check that you are using the correct Internet connection.
- Check the routing table to see which routing tag is used by the provider’s Internet connection (in the menu IP Router → Routing → IPv4 routing table).
- The identical routing tag has to be entered in the SIP-line configuration (in the menu Voice Call Manager → Lines → SIP lines on the Advanced tab).