With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
bstunRouteSerial
Cisco Blocked Serial Tunneling Route Serial
1.3.6.1.4.1.9.9.35.1.4.1.1.5
If bstunRouteType is serial then this is the serial interface index of the point-to-point link to the remote partner; if bstunRouteType is serialDirect then the partner is in the local BSTUN. if bstunRouteType is ip then this field is 0.
Back to CISCO-BSTUN-MIB MIB page.
IPHost Network monitor allows you to monitor bstunRouteSerial 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.