NAT-T was not supported on the PIX firewall till december last year (that was when I looking for this functionality). This is a new feture and only 6.3 seems to support it (and some 6.2 images such as 6.2(2.132) ). What you need to do is to make sure that the image running on your firewall supports NAT-T.
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...