You can monitor and clear the VPN session counters or statistics in a Cisco ASA Firewall using: show vpn-sessiondb summary and clear vpn-sessiondb statistics global commands, respectively.
ciscoasa# show vpn-sessiondb summary
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VPN Session Summary
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Active : Cumulative : Peak Concur : Inactive
----------------------------------------------
AnyConnect Client : 0 : 660 : 2 : 0
SSL/TLS/DTLS : 0 : 660 : 2 : 0
IKEv1 IPsec/L2TP IPsec : 0 : 206 : 5
Site-to-Site VPN : 7 : 50169 : 11
IKEv1 IPsec : 7 : 50169 : 11
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Total Active and Inactive : 7 Total Cumulative : 51035
Device Total VPN Capacity : 250
Device Load : 3%
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ciscoasa# clear vpn-sessiondb statistics global
INFO: Global session data cleared
ciscoasa# show vpn-sessiondb summary
No sessions to display.
Statistics have been cleared 1 time(s) since reboot
ciscoasa# show vpn-sessiondb summary
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VPN Session Summary
---------------------------------------------------------------------------
Active : Cumulative : Peak Concur : Inactive
----------------------------------------------
AnyConnect Client : 0 : 660 : 2 : 0
SSL/TLS/DTLS : 0 : 660 : 2 : 0
IKEv1 IPsec/L2TP IPsec : 0 : 206 : 5
Site-to-Site VPN : 7 : 50169 : 11
IKEv1 IPsec : 7 : 50169 : 11
---------------------------------------------------------------------------
Total Active and Inactive : 7 Total Cumulative : 51035
Device Total VPN Capacity : 250
Device Load : 3%
---------------------------------------------------------------------------
ciscoasa# clear vpn-sessiondb statistics global
INFO: Global session data cleared
ciscoasa# show vpn-sessiondb summary
No sessions to display.
Statistics have been cleared 1 time(s) since reboot