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Cisco CSS 11000 Series Content Services Switches

Load Balancing FTP Servers on CSS 11000 Products

Document ID: 12615

Updated: Jan 02, 2007

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Introduction

This document outlines the difference between the two FTP modes (PORT-PASV) and how they apply to source groups on the Content Services Switch (CSS). The FTP control connection is initiated by the FTP client that wants to connect to the FTP server. The control connection is used to issue commands to the FTP server and to get simple responses. However, the actual file transfer takes place over a separate data connection. The data connection may be initiated by the FTP client or the FTP server; these different modes of FTP are referred to as the PORT (active) mode and PASV (passive) mode. The FTP client decides which mode to use.

Prerequisites

Requirements

There are no specific prerequisites for this document.

Components Used

The information in this document is based on all Cisco CSS 11000 Series Content Services Switches and Cisco WebNS Software Release 3.02 and later.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for information on document conventions.

PORT Mode FTP

This is the process in PORT mode:

  1. The client issues the retrieval request.

  2. The client sets up the listening port.

  3. The client issues a PORT command to the FTP server that informs the server which port the client listens to for the data connection.

  4. The server establishes the connection to the address indicated by the PORT command.

PASV Mode FTP

This is the process in PASV mode:

  1. The client issues the retrieval request.

  2. The client issues the PASV command to the server and indicates that it wants the server to go to the passive mode.

  3. The server sets up a listening port.

  4. The server responds and lets the client know which port it listens to for the data connection.

  5. The client establishes the connection to the address indicated in the response from the server to the PASV command.

The default FTP mode on Internet Explorer (IE) and Netscape is PASV mode. When you FTP from the DOS prompt on a Windows-based system, PORT mode is used.

Load Balancing FTP Servers

When load balancing FTP servers, a source group is necessary. When you FTP to a Virtual IP (VIP) address, the source group ensures that the VIP address is sent to the client (not the actual IP address of the backend FTP server, which is what happens if you do not use a source group). You must also specify the application type as ftp-control.

Related Information

Updated: Jan 02, 2007
Document ID: 12615