Citrix ADC

Load balance a group of FTP servers

The Citrix ADC appliance can be used to load balance FTP servers. FTP requires that the user initiate two connections on two different ports to the same server: the control connection, through which the client sends commands to the server, and the data connection, through which the server sends data to the client. When the client initiates an FTP session by opening a control connection to the FTP server, the appliance uses the configured load balancing method to select an FTP service, and forwards the control connection to it. The load balanced FTP server then opens a data connection to the client for information exchange.

The following diagram describes the topology of a load balancing configuration for a group of FTP servers.

Figure 1. Basic Load Balancing Topology for FTP Servers

LB FTP servers

In the diagram, the services Service-FTP-1, Service-FTP-2, and Service-FTP-3 are bound to the virtual server Vserver-LB-1. Vserver-LB-1 forwards the client’s connection request to one of the services using the least connection load balancing method. Subsequent requests are forwarded to the service that the appliance initially selected for load balancing.

The following table lists the names and values of the basic entities configured on the appliance.

Entity type Name IP address Port Protocol
Vserver Vserver-LB-1 21 FTP
Services Service-FTP-1 21 FTP
  Service-FTP-2 21 FTP
  Service-FTP-3 21 FTP
Monitors FTP None None None

The following diagram shows the load balancing entities, and the values of the parameters that need to be configured on the appliance.

Figure 2. Load Balancing FTP Servers Entity Model

FTP entity model

The appliance can also provide a passive FTP option to access FTP servers from outside of a firewall. When a client uses the passive FTP option and initiates a control connection to the FTP server, the FTP server also initiates a control connection to the client. It then initiates a data connection to transfer a file through the firewall.

To create services and virtual servers of type FTP, see Setting Up Basic Load Balancing. Name the entities and set the parameters to the values described in the columns of the previous table. When you configure a basic load balancing setup, a default monitor is bound to the services.

Next, bind the FTP monitor to the services by following the procedure described in the section Binding Monitors to Services.

To create FTP monitors by using the CLI

At the command prompt, type:

add lb monitor <MonitorName> FTP -interval <Interval> -userName <UserName> -password <Password>


add lb monitor monitor-FTP-1 FTP -interval 360 -userName User -password User

To create FTP monitors by using the GUI

  1. Navigate to Traffic Management > Load Balancing > Monitors.
  2. Create a monitor of type FTP, and in Special Parameters, specify a user name and password.
Load balance a group of FTP servers