With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
natSessionPrivateSrcAddr
nat Session Private Src Addr
1.3.6.1.2.1.123.1.9.1.11
The source IP address of the session endpoint that lies in the private network. The value of this object must be zero only when the natSessionPrivateSrcEPBindId object has a zero value. When the value of this object is zero, the NAT session lookup will match any IP address to this field. The type of this address is determined by the value of the natSessionPrivateAddrType object.
Back to NAT-MIB MIB page.
IPHost Network monitor allows you to monitor natSessionPrivateSrcAddr on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco switches right now.