Filter
Top Products
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
Windows 2000 White Paper
37