Updating root hints

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Updating root hints

Root hints are used to prepare servers authoritative for non-root zones so that they can learn and discover authoritative servers that manage domains located at a higher level or in other subtrees of the DNS domain namespace. These hints are essential for servers authoritative at lower levels of the namespace when locating and finding servers under these conditions.

For example, suppose a DNS server (Server A) has a zone called sub.example.microsoft.com. In the process of answering a query for a higher-level domain, such as the example.microsoft.com domain, Server A needs some assistance to locate an authoritative server (such as Server B) for this domain.

In order for Server A to find Server B, or any other servers that are authoritative for the microsoft.com domain, it needs to be able to query the root servers for the DNS namespace. The root servers can then refer Server A to the authoritative servers for the com domain. The servers for the com domain can, in turn, offer referral to Server B or other servers that are authoritative for the microsoft.com domain.

The root hints used by Server A must have helpful hints to the root servers for this process to locate Server B (or another authoritative server) as intended.

To configure and use root hints correctly, first determine how the following applies to your DNS servers:

  • Are you using DNS on the Internet or on a private network?

  • Is the server used as a root server?

By default, the DNS Server service implements root hints using a file, Cache.dns, stored in the systemroot\System32\Dns folder on the server computer. This file normally contains the NS and A resource records for the Internet root servers. If, however, you are using the DNS Server service on a private network, you can edit or replace this file with similar records that point to your own internal root DNS servers.

Another server configuration in which root hints are treated differently is one in which a DNS server is configured to be used by other DNS servers in an internal namespace as a forwarder for any DNS queries of names managed externally (the Internet, for example). Even though the DNS server used as a forwarder can be located internally on the same network as servers using it as a forwarder, it needs hints for the Internet root servers to work properly and resolve external names.

To update root hints, see Update root hints on the DNS server.


  • If you are operating internal root servers, do not use root hints. Instead, delete the Cache.dns file entirely for any of your root servers.

  • If a DNS server is configured to know about other DNS servers, such as through a list of DNS servers configured in its client TCP/IP properties for an installed network connection, the DNS Server service is capable of gathering its own root hints during new server configuration. You can use the Configure a DNS Server Wizard provided with the DNS console to accomplish this.