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Case Study: An Error Message is Displayed when nslookup Utility is used to Point to a NetScaler Appliance

  • CTX126357
  • Created On  Aug 20, 2010
  • Updated On  Mar 10, 2012
  • Article
  • Topic : Load Balancing/High Availability

Problem Definition

A customer had configured Domain Name System (DNS) Load Balancing virtual server (VServer). The customer reported that when the nslookup utility was used from the Windows operating system to point to the NetScaler appliance, the following error message was displayed:

Can't find server name for address Non-existent domain
Default servers are not available
Default Server: UnKnown

The customer wanted to display the default server name for the NetScaler appliance when using the nslookup utility.

Note: The customer informed that the DNS virtual IP (VIP) address responds to the DNS queries appropriately.

Troubleshooting Methodology

The Citrix Technical Support Engineers verified that when using the nslookup utility from the Windows operating system, the error messages mentioned in the Problem Definition section was displayed.


This error message is displayed when you have not defined a pointer (PTR) record for the IP address of the name server. When the nslookup utility starts, it performs a reverse lookup to get the name of the default server. If no PTR record exists, the error message is displayed.


To resolve this issue, the engineers advised the customer to ensure that a reverse lookup zone exists and contains PTR records for the name server.

To add a PTR record on a NetScaler appliance, complete the following procedure:

  1. In the Navigation pane, expand the DNS node.
  2. Expand the Records node.
  3. Click PTR Records.
  4. On the PTR Records page, click Add.
  5. In the IP Address field, type the IP address, such as, that the PTR record should point to.
  6. In the Domain field, type the domain name, such as, that you want to reverse map.
  7. Click Add.
  8. Click Create.
  9. Click Close.

Alternatively, you can run the following command from the command line interface of the appliance to add a PTR record:

> add dns ptrRec

Additional Information

Refer to the [url]List of DNS record types[url] Wikipedia page for more information on the DNS record types.

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