Proxy arp is needed when you are natting because the Natted IP is not physically given to some interface, the arp requests coming from the users will have to be answered by the firewall becuase the natted ip is configured on it.
Basically, when the clients send an ARP request for the Natted IP, the firewall says that "OK, I have this IP---So i will reply on its behalf"
Proxy arp is essential especially if the Natted subnet does not belong to the firewall itself. i.e. the natted ip range is not given on any interface of the firewall.
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...