With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
alL2tpStatsSessionRecvDiscards
ALTIGA L2tp Statistics Session Receive Discards
1.3.6.1.4.1.3076.2.1.2.16.3.1.27
This object returns the total number of payload packets received that were discarded for this session.
Back to ALTIGA-L2TP-STATS-MIB MIB page.
IPHost Network monitor allows you to monitor alL2tpStatsSessionRecvDiscards 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.