Out of the box, most IPSec tunnels don't have any authentication to use them - whatever ip address is allowed to make a connection through the tunnel can do so. Cisco does have some proprietary features to allow some auth before using the tunnel.
Use syslog. Then configure rules on your syslog server to forward an alert to a "who's logged on" mailbox when someone logs onto a resource locally. Or you could just have it write those logons to a seperate file (kiwi syslog supports this) and refer to it as necessary.
You could also serve up those log files on a webserver so you could just check a webpage to see who is on.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...