Configure a Caching-Only DNS Server

All DNS servers resolve queries and then cache the results of queries for a limited time. They also perform other functions such as updating records and doing zone database maintenance. You might want a server that simply resolves queries and caches the results. A caching-only server is especially useful when DNS resolution is needed but when you don't want to create a separate zone for that location.

With a caching-only server, query information is gathered over time from other DNS servers as the caching-only server resolves client queries. That information is then stored by the caching-only server for future use. This process usually results in a decreasing amount of network traffic over time between the location containing the caching-only server and those other locations that contain full-version DNS zones. The benefit comes in the reduced use of the WAN link for DNS resolution while increasing name resolution performance for the local clients. The caching-only server does not perform zone transfers like other DNS servers, and so the WAN is not impacted by this traffic.

1. On the server where you want to configure the DNS caching-only server, open DNS Manager.
2. Right-click the name of the server, and select Configure A DNS Server.
3. Choose to configure the root hints only. Do not configure a forward or reverse lookup zone.
4. Click Finish.

This process really could not be much easier. You now have a caching- only DNS server that will take client requests and perform recursive DNS name queries. When the server resolves a query, it will store the answer locally. There are no zones to maintain or update. No zone transfers are necessary, and the clients get the benefit of a local DNS server.

Manage Root Hints

We know some of you out there are scratching your heads and thinking, "What in the world is a root hint?" By definition, a root hint is a piece of DNS data stored in the DNS database that identifies the authoritative servers for the root of a given DNS namespace. If you want to resolve a query for a namespace, you have to find the server responsible for resolving requests for that space. DNS names are hierarchical in structure, and each level of the hierarchy is separated by a period (or a dot). So, for example, if you had a client who was trying to resolve the hierarchical name www.microsoft.com, you would begin the process at the root, which in this case is com. Where is the com server? Wouldn't it be nice if you already had a list of commonly used roots (like com, mil, gov, edu, net, org, and so on) and their corresponding IP addresses? These are the root hints.

By default DNS contains a standard list of commonly used root hints. The root hints contain the name server (NS) records and the host (A) resource records for the internet root servers. All of this works very well if you are on the Internet. What if you are on a private network and want to configure your own root servers? You can configure your own root zone and add the associated NS and A records to root hints as follows:

1. Open DNS Manager.
2. Right-click your DNS server, and choose Properties.
3. Select the Root Hints tab.

At this point you can add, edit, or remove root hints, or you can choose to copy the root hints from another server.