The default PRTG sensor for VPN connections on a Cisco ASA has a limited of 50 users connected, actually less. This is due to the limit of 50 channels per sensor.
These days IT departments everywhere likely exceed 50 VPN users everywhere.
Since I do not need to know who is connected, rather then the amount and load on the FW, I came up with a simple sensor and MAP in PRTG to show me the essentials.
Add a snmp custom sensor to your FW in PRTG and use the OID
This will give you a number of VPN connection. I am not 100% certain about the OID only being used for Cisco AnyConnect or other VPNs as well. I found it as a valid SNMP OID as I only use Cisco AnyConnect and my VPN tunnels aligned with this number.
Further did I add sensors for CPU / RAM and on the external interface of the FW to the map in PRTG to see the overall status and load.
Detailed information on the bandwidth are a different story, since this is more a passive point in time configuration, I don’t pull that in this map – I care about an average load picture not single pikes that only are temporarily. For this I have different approaches and sources. Mentioning this only for the big picture and cause you need to be aware of that.
Hope some find this helpful.
If you want the users that are online and offline – what is actually a big of a questionable thing due to data privacy concerns and a user not always needing to be on VPN in order to do work – you could create scrips to access more detailed SNMP data and balance this in various sensors. This is possible, but I do not recommend it. Another approach would be using the TEXT value in XML sensors and put the info there. Still, I think you might get to much data and need to ask yourself if this is even something you should collect/monitor.
Here a picture of my map as we barely started getting more home office people online.
Backlink to the Paessler PRTG KB, where this was discussed as well: https://kb.paessler.com/en/topic/64053-my-snmp-cisco-asa-vpn-users-sensor-shows-a-user-limit-error-why-what-can-i-do