Cause: The firewall is blocking incoming IP packets

Many routers interrupt the forwarding of incoming UDP packets if there is no activity for a certain period of time (e.g. after 30 seconds by default with Cisco). As a result, our telephone server can no longer reach your telephone system and incoming calls are not delivered.

The connection is only re-established when there is an action from your internal network to the phone server - such as a new outgoing call, a new registration or a NAT keep-alive.

Measures in the event of occasional loss of registration

There are various ways to open the firewall or keep it permanently open:

Release registrar in the firewall

Put your registrar on the whitelist in your firewall. Please do not enter the IP address of our telephone server in the firewall, as this may change.

Product Registrar
SIP Trunk / VoIP sip.easybell.com
Cloud PBX pbx.easybell.de

Increase UDP timeout

If whitelisting is not possible, check the UDP timeout of your firewall.

Increase the UDP timeout until it exceeds the duration of the registration or NAT keepalive.

Reduce NAT Keepalive

If the UDP timeout cannot be increased, reduce the NAT keepalive until it is below the UDP timeout.

Reduce register duration

If all of the above measures are not possible, reduce the register duration.

Please note that the re-register must not be less than 600 seconds.

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Created on: 24. October 2025