With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
x21LineNumofValidEntries
x21 Line Numof Valid Entries
1.3.6.1.4.1.351.110.4.5.1.2
The number of X.21/HSSI configuration entries (regardless of their current configuration) in the x21ConfigTable table.
Back to CISCO-WAN-FR-X21-MIB MIB page.
IPHost Network monitor allows you to monitor x21LineNumofValidEntries 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.
