The same-security-traffic intra-interface command lets traffic enter and exit the same interface, which is normally not allowed. This feature might be useful for VPN traffic that enters an interface, but is then routed out the same interface. The VPN traffic might be unencrypted in this case, or it might be reencrypted for another VPN connection. For example, if you have a hub and spoke VPN network, where the security appliance is the hub, and remote VPN networks are spokes, for one spoke to communicate with another spoke, traffic must go into the security appliance and then out again to the other spoke.
I have seen issues where spoofed traffic created bogus conns with intra-interface configured. For example, source 192.168.1.10 destined: 184.108.40.206 on the outside interface. This traffic gets u-turned and if a packet for 192.168.1.10 enters the firewall on the inside it will be dropped because there is already a conn built on the outside interface.
The general recommendation is "don't use it if it's not absolutely necessary"
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...