Device Located behind NAT

Two different streams of traffic traverse through NAT - signaling and media. A device located behind NAT that initiates a signaling path has problems receiving incoming signaling responses, as they are blocked by the NAT server. Therefore, the initiating device must inform the receiving device where to send the media. To resolve this NAT problem, the device provides the following solution:

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NAT Translation table, which configures NAT per IP network interface - see Configuring NAT Translation per IP Interface.

If NAT is not configured, the device sends the packet according to its IP address configured in the IP Interfaces table.

The figure below illustrates the NAT problem faced by SIP networks when the device is located behind a NAT: