Brekeke SIP Server Wiki

Configuration for Far-End NAT traversal

To communicate properly with SIP clients located behind a NAT over the Internet, Far-End NAT traversal feature is applied to the call. If the Brekeke SIP Server is located behind a different NAT, you would need to set the Near-End NAT traversal setting as well.


Far-End NAT traversal requires maintaining port mapping at the router that is located at the same network with SIP clients. SIP packets from the Brekeke SIP Server will be undeliverable when port mapping has been cleared. To ensure maintaining the port mapping at the router, the Brekeke SIP Server needs to send dummy SIP packets for refreshing periodically; this feature is called Keep Alive. The interval of Keep Alive needs to be set short to prevent port mapping being cleared.

For some routers, this Keep Alive feature does not work to maintain port mapping. For such a case, we recommend that you use the Port Forwarding setting at the router instead. Please refer to the step.2.

In the [Configuration] page > [SIP], set [NAT traversal] as follows.

Item Setting Value Explanation
Keep address/

port mapping

on Enable Keep Alive feature
Interval (ms) (Depends on network environments.) This is the interval to send dummy SIP packets. Default is set as 12,000 milliseconds (12 seconds). Shorter interval is recommended to ensure maintaining port mapping at routers.


In addition to the Keep Alive feature, there is another way to establish communications with a SIP client located behind a NAT over the Internet. When the communication cannot be established, even with Keep Alive settings, it is necessary to set port forwarding settings on the router located on the same network with SIP client. For port forwarding, you need to set the port numbers for SIP and RTP that SIP client is using on the router. Please refer to the configuration screen or document of SIP client for the port numbers to set at these settings.

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