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A client might have multiple network adapters and thus might have multiple IP
addresses. That could theoretically put the client in multiple sites. The design above
ignores this remote possibility. Rather, it assumes that the client is in the site
corresponding to the adapter, which was used to ping one of the DCs. To handle
the case where this ambiguity is detrimental, NetLogon allows the site name to be
manually configured by setting the REG_SZ value SiteName under the Registry key
HKLM\System\CurrentControlSet\Services\NetLogon\Parameters. If this parameter
is defined, the Site Name of the machine is forced to be the specified value and the
site name dynamically discovered from Active Directory by the locator will never be
used.
Caching Resolver
The Windows 2000 implementation of DNS introduces a client-side caching
resolver for DNS name resolution. Caching resolver is a Windows 2000 service with
the sole purpose of improving name lookup performance, and reducing network
traffic associated with name lookups by minimizing the number of name resolution
round trips.
Caching resolver runs in the context of the Services.exe process (Service Control
Manager) and can be turned on and off just like any other service.
The Windows 2000DNS caching service includes the following features:
• General caching of queries.
• Negative caching.
• Removal of previously resolved names from the cache based on negative
acknowledgement.
• Keeping track of transient (Plug and Play) network adapters and their IP
configuration.
• Keeping a record of each adapter’s DomainName.
• Management of unresponsive name servers.
• The caching resolver cash can be purged using the IPCONFIG command.
• An ability to prioritize multiple A RRs returned from the DNS server based on
their IP address. If the resolver sends a query specifying such prioritization,
then the DNS server finds the A records with IP addresses from the networks
which the computer is directly connected to and places them first in its
response. This feature prevents Round Robin from working properly. It can be
disabled through the Registry.
• Accepting response from non-queried IP address (This feature is enabled by
default. It can be disabled through the Registry).
• An ability to automatically reload the updated local Hosts file into the resolver’s
cache. Thus, as soon as a Hosts file is changed the resolver’s cache is
updated.
• An ability to initiate a network failure timeout. If all resolver’s queries are timed
out then it assumes the network failure and does not submit any queries for a
certain period (30 seconds by default) of time. In case of a multi-adapter
Windows 2000 White Paper 36