With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cdxCpeToCmInetAddress
Cisco DOCSIS Cpe To Cable Modem Inet Address
1.3.6.1.4.1.9.9.116.1.3.9.1.4
This object identifies the address assigned to this cable modem.
Back to CISCO-DOCS-EXT-MIB MIB page.
IPHost Network monitor allows you to monitor cdxCpeToCmInetAddress on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco wireless switches right now.