Product Documentation

Configuring the NetScaler as an End Resolver

Aug 31, 2016

A resolver is a procedure that is invoked by an application program that translates a domain/host name to its resource record. The resolver interacts with the LDNS, which looks up the domain name to obtain its IP address. The NetScaler can provide end-to-end resolution for DNS queries.

In recursive resolution, the NetScaler appliance queries different name servers recursively to access the IP address of a domain. When the NetScaler receives a DNS request, it checks its cache for the DNS record. If the record is not present in the cache, it queries the root servers configured in the ns.conf file. The root name server reports back with the address of a DNS server that has detailed information about the second-level domain. The process is repeated until the required record is found.

When you start the NetScaler appliance for the first time, 13 root name servers are added to the ns.conf file. The NS and Address records for the 13 root servers are also added. You can modify the ns.conf file, but the NetScaler does not allow you to delete all 13 records; at least one name server entry is required for the appliance to perform name resolution. The following diagram illustrates the process of name resolution.

Figure 1. Recursive Resolution


In the process shown in the diagram, when the name server receives a query for the address of s1.s2.s3.com, it first checks the root name servers for s1.s2.s3.com. A root name server reports back with the address of the .com name server. If the address of s1.s2.s3.com is found in the name server, it responds with a suitable IP address. Otherwise, it queries other name servers for s3.com, then for s2.s3.com to retrieve the address of s1.s2.s3.com. In this way, resolution always starts from root name servers and ends with the domain’s authoritative name server.

Note: For recursive resolution functionality, caching should be enabled.
This document includes the following information:

Enabling Recursive Resolution

Updated: 2013-08-27

To configure the NetScaler appliance to function as an end resolver, you must enable recursive resolution on the appliance.

To enable recursive resolution by using the command line interface

At the command prompt, type the following commands to enable recursive resolution and verify the configuration:

  • set dns parameter -recursion ENABLED
  • show dns parameter

Example

 
> set dns parameter -recursion ENABLED 
 Done 
> show dns parameter 
        DNS parameters: 
			. 
			. 
			. 
        Recursive Resolution : ENABLED 
			. 
			. 
			. 
 Done 
> 

To enable recursive resolution by using the configuration utility

  1. Navigate to Traffic Management > DNS.
  2. In the details pane, under Settings, click Change DNS settings.
  3. In the Configure DNS Parameters dialog box, select the Enable recursion check box, and then click OK.

Setting the Number of Retries

Updated: 2013-08-27

The NetScaler appliance can be configured to make a preconfigured number of attempts (called DNS retries) when it does not receive a response from the server to which it sends a query. By default, the number of DNS retries is set to 5.

To set the number of DNS retries by using the command line interface

At the command prompt, type the following commands to set the number of retries and verify the configuration:

  • set dns parameter -retries <positive_integer>
  • show dns parameter

Example

 
> set DNS parameter -retries 3 
 Done 
> show dns parameter 
        DNS parameters: 
        DNS retries: 3 
			. 
			. 
			. 
 Done 
> 

To set the number of retries by using the configuration utility

  1. Navigate to Traffic Management > DNS.
  2. In the details pane, under Settings, click Change DNS settings.
  3. In the Configure DNS Parameters dialog box, in the DNS Retries text box, type the DNS resolver request retry count, and then click OK.