With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cipIpInDiscards
Cisco Channel Interface Processor Ip In Discards
1.3.6.1.4.1.9.9.32.1.1.1.1.9
The number of input IP datagrams for which no problems were encountered to prevent their continued processing, but which were discarded (e.g., for lack of buffer space). Note that this counter does not include any datagrams discarded while awaiting re-assembly.
Back to CISCO-CIPTCPIP-MIB MIB page.
IPHost Network monitor allows you to monitor cipIpInDiscards 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.