I am having the exact same problem. I have ran a tcpdump to see what is going on and have noticed that ACS is not even attempting to connect to the sftp server at all. When adding the crypto key I do see the successful exchange, but no traffic whatsoever when trying to connect to the sftp server.
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...