As per Cisco doc, all VPN 3000 Concentrators works as a VPN Server or VPN termination point for all supported incoming VPN connection, i.e IPSec VPN, L2TP, etc.
Basically it controls all clients (Cisco VPN Client software or hardware, Microsoft L2TP) or access for site-to-sire/LAN-to-LAN (using router or firewall), but the box itself has no feature to act like a client or peer to establish VPN link to any client devices like server.
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...
[toc:faq]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 and UDP are I...