FTP uses two ports, one for control and one for data. The client initiates a session on the server's control port (tcp:21), then the server initiates a session to the client from its data port (tcp:20). You just need to allow port 21 inbound, the port 20 session is established outbound to the requesting client.
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...