With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
rprSpanCurrentInMcastClassAOctets
rpr Span Current In Mcast Class A Octets
1.0.8802.17.1.1.1.3.1.1.12
The number of received (PHY to MAC) classA multicast and broadcast octets in the current interval.
Back to IEEE-802DOT17-RPR-MIB MIB page.
IPHost Network monitor allows you to monitor rprSpanCurrentInMcastClassAOctets 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.