Traffic across firewalls passes through the access rules. In PIX devices, single ACL is matched to a traffic, whereas in Cisco ASA 5500, traffic is matched to two ACL's (ingress and egress ACL). I have come across these in the below Cisco NSEL document
Not strictly accurate. Pix v6.x and before did not support outbound acls on an interface. However Pix v7.x and onwards does support outbound acls so both the ASA and Pix (v7.x onwards) support both outbound and inbound acls.
When to use outbound acls really depends on your requirements. Most times you can use inbound acls but outbound can be useful in certain situations.
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...