Negative Caching

In addition to caching resolved queries, resolvers and servers can also cache negative responses, that is, the information that a specific resource record set (RRset) or DNS domain name does not exist. Negative caching can reduce the response time for negative answers. It can also reduce network traffic by reducing the number of messages that must be sent between resolvers and name servers or between name servers.

Negative caching is specified in RFCs 1034 and 2308. RFC 1034 describes how to cache negative responses and makes negative caching optional. RFC 2308 requires resolvers to cache negative responses if they cache any responses. It also describes a way for name servers to forward cached negative responses to resolvers. Just as with ordinary caching, they must also start decreasing the TTL.

For more information about negative caching with Windows 2000 DNS, see "Windows 2000 DNS" in this book.