Load balance DNS servers

When you request DNS resolution of a domain name, the Citrix ADC appliance uses the configured load balancing method to select a DNS service. The DNS server to which the service is bound then resolves the domain name and returns the IP address as the response. The appliance can also cache DNS responses and use the cached information to respond to future requests for resolution of the same domain name. Load balancing DNS servers improves DNS response times.

The following diagram describes the topology of a load balancing configuration that load balances a group of DNS services.

Figure 1. Basic Load Balancing Topology for DNS Servers


In the diagram, the services Service-DNS-1, Service-DNS-2, and Service-DNS-3 are bound to the virtual server Vserver-LB-1. The virtual server Vserver-LB-1 forwards client requests to a service using the least connection load balancing method. The following table lists the names and values of the basic entities configured on the appliance.

Entity type Name IP address Port Protocol
Virtual Server Vserver-LB-1 53 DNS
Services Service-DNS-1 53 DNS
  Service-DNS-2 53 DNS
  Service-DNS-3 53 DNS
Monitors monitor-DNS-1 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 DNS Servers Entity Model


To configure a basic DNS load balancing setup, see Setting Up Basic Load Balancing. Follow the procedures to create services and virtual servers of type DNS, naming the entities and setting the parameters using the values described in the previous table. When you configure a basic load balancing setup, the default ping monitor is bound to the services. For instructions on binding a DNS monitor to DNS services, you can also see Binding Monitors to Services. The following procedure describes the steps to create a monitor that maps a domain name to the IP address based on a query.

To configure DNS monitors by using the command line interface

At the command prompt, type:

add lb monitor <monitorName> DNS -query <domainName> -queryType <Address|ZONE> -IPAddress <ipAddress>


add lb monitor monitor-DNS-1 DNS -query -queryType Address -IPAddress

add lb monitor monitor-DNS-2 DNS -query -queryType Address -IPAddress

To configure DNS monitors by using the configuration utility

  1. Navigate to Traffic Management > Load Balancing > Monitors.
  2. Create a monitor of type DNS, and in Special Parameters, specify a query and query type.
Load balance DNS servers