White Paper Abstract:
This paper summarizes that Cisco IOS® Software Releases 11.2(13) and 11.3(3) introduced the functionality for Network Address Translation (NAT) to support non−standard File Transfer Protocol (FTP) port numbers. In earlier Cisco IOS software releases, when a NAT−enabled router receives a packet with IP addresses that need to beNAT−translated, and the standard TCP port number is for the FTP control connection (21), the router recognizes the packet as an FTP packet, and does any necessary translation in the payload (data portion) of thepacket. However, if the FTP server is using a non−standard FTP port number, NAT ignores the payload of the packet. This can prevent FTP data connections from being established.