Traffic arrives to Public_IP How firewall should know to which inside IP forward traffic? private_IP_1 or private_IP_1 ??? So its reason why its not possible to have 1 public Ip to 2 private IP mappings....
BUT you can use port forwarding... Let we say you have one public IP and two private servers (FTP and WWW) so you can forward FTP traffic to one server and www traffic to second server
You can achieve that provided you mapped the 2 public IP to one internal IP to a different port, i.e 1st public IP is to provide access to WWW (tcp 80), while the 2nd public IP is to allow access to FTP (TCP 21) and so on.
Make sure they don't clashed or use same port number:
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...