With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cGgsnExtSubscriberMSAddr
cisco Gateway GPRS Support Node Ext Subscriber MS Address
1.3.6.1.4.1.9.9.647.1.1.18.1.4
This object indicates the inet address of the Subscriber.
Back to CISCO-GGSN-EXT-MIB MIB page.
IPHost Network monitor allows you to monitor cGgsnExtSubscriberMSAddr on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco routers right now.