Microsoft windows 2000 DNS manual Fully-Qualified Query, Name Resolution

computer, the same rule is applicable to every adapter separately. This feature is enabled by default. It can be disabled through the Registry.

Name Resolution

A basic name resolution request consists of a query for a given type of a DNS record with a given DNS name. The name to be resolved supplied in a query falls into one of three categories:

•Fully qualified. The name specified in the query is dot-terminated.

•Unqualified Single-Label. The name specified in the query contains no dots.

•Unqualified Multi-Label. The name specified in the query contains a dot(s), but is not dot-terminated.

Fully-Qualified Query

A fully-qualified name uniquely identifies a particular machine on the network and requires no alterations, for example ntserver.mydomain.microsoft.com.

If such a name needs to be resolved, first a caching resolver tries to resolve the fully-qualified query against its cache (note that the HOSTS file is preloaded in the resolver cache). If it fails then the fully-qualified query is sent directly to a DNS server. The caching resolver learns of lists of DNS servers it can query through the TCP/IP configuration of the local machine. A machine with multiple adapters may have multiple DNS server lists.

The adapters on a multi-homed machine may or may not be participating in a fully- connected network. If the networks are disjoint, the DNS namespaces on those adapters may also be disjoint. For this reason, queries must be sent to DNS servers on all adapters for complete name resolution. The response to a query can be grouped into one of four classes:

•A positive answer. The name exists and has data associated with it.

•A negative answer. The name does not exist, or the name exists, but with no associated data.

•A server failure. The server cannot service the request.

•No answer. The server does not answer within the timeout period.

The DNS servers in a list associated with a particular adapter are assumed to be members of the same namespace. Servers are queried in the order they are given in the list, which is defined by the servers priorities. If one server in the list returns a positive or negative answer, then no other servers in that list are posed the same question. The resolver may advance to the remaining servers in the list only if the current server does not respond or responds with a server failure (this scenario is slightly different for a multi-homed machine, as shown below). Should a server not respond, the resolver dynamically reorders the list changing the priority of the non- responding server (for more detailed information on this see the section on “DNS Server List Management”).

For efficiency, one fast adapter is considered the preferred adapter for name

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