A CGN device generates NAT logs according to the following mechanisms:
1. Based on the session NAT 5-tuple (source IP address, sink IP address, source port, sink port, and protocol ID), a NAT log is generated upon a change of the source or sink port even if the sink and source IP addresses do not change. As result, a large number of NAT logs may be generated.2. Based on port blocks, only one NAT session log is generated if the source port varies within the pre-allocated port blocks when the source IP address, source IP address, sink port, and protocol ID do not change.