The nat outside option lets you enable or disable outside NAT, which translates the source address of a connection coming from a lower security interface to higher interface. This feature is also called bidirectional NAT.If you enable outside dynamic NAT on an interface, then you must configure explicit NAT policy for all hosts on the interface that need to initiate connections to inside networks. If you want to translate some hosts, but not others, then use identity NAT or NAT exemption (nat 0 or nat 0 access-list) to disable address translation for these additional hosts. The norandomseq and emb_limit options are not supported with outside NAT.
Use the following url to get more info about configuring outside(bidirectional) NAT on PIX:
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...