With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
rprSpanErrorCurrentSelfSrcUcastFrames
rpr Span Error Current Self Source Ucast Frames
1.0.8802.17.1.1.1.5.1.1.8
The number of received (PHY to MAC) unicast frames that were transmitted by the station itself i.e. the source MAC is equal to the interface MAC.
Back to IEEE-802DOT17-RPR-MIB MIB page.
IPHost Network monitor allows you to monitor rprSpanErrorCurrentSelfSrcUcastFrames on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.