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Aging/Scavenging Terminology

The aging and scavenging process is a new feature in Windows 2000 Server. The following table indicates new or revised terms that have been introduced to help specifically when discussing these features.

Table 1

Aging/Scavenging Terminology

Term

Description

Resource record (RR) time stamp

A date and time value used by the DNS server to determine the removal of the resource record when it performs aging and scavenging operations.

Current server time

The current date and time on the DNS server. This number can be expressed as an exact numeric value at any point in time.

No-refresh interval

An interval of time, determined for each zone, as bounded by the following two events:

  • The date and time when the record was last refreshed and its time stamp set.

  • The date and time when the record next becomes eligible to be refreshed and have its time stamp reset.

This value is needed to decrease the number of write operations to the Active Directory database. By default, this interval is set to 7 days. It should not be increased to an unreasonably high level because the benefits of the aging and scavenging feature might either be lost or diminished.

Refresh interval

An interval of time, determined for each zone, as bounded by the following two distinct events:

  • The earliest date and time when the record becomes eligible to be refreshed and have its time stamp reset.

  • The earliest date and time when the record becomes eligible to be scavenged and removed from the zone database.

This value should be large enough to allow all clients to refresh their records. By default, this interval is set to 7 days. It should not be increased to an unreasonably high level, because the benefits of the aging and scavenging feature might either be lost or diminished.

Start scavenging time

A specific time, expressed as a number. The server uses this time to determine when a zone becomes available for scavenging. For more information, see the next section, "When Scavenging Can Start."

Scavenging period

When automatic scavenging is enabled at the server, this period represents the time between repetitions of the automated scavenging process. The default value for this is seven days. To prevent deterioration of DNS server performance, the minimum allowed value for this is one hour.

Record refresh

When a DNS dynamic update is processed for a resource record when only the resource record time stamp, and no other characteristics of the record, are revised.

Refreshes generally occur for the following reasons:

  • When a computer is restarted on the network and, if at startup, its name and IP address information are consistent with the same name and address information it used prior to being shut down, it sends a refresh to renew its associated resource records for this information.

  • A periodic refresh is sent by the computer while it is running. For Windows 2000, all computers renew DNS registration of their associated resource records every 24 hours. When this renewal attempt occurs, if the same DNS name and IP address mappings information are in effect, the resulting update request is considered to be a refresh and not a resource record update.

  • Other network services make refresh attempts, such as DHCP servers, which renew client address leases; cluster servers, which register and update records for a cluster; and the Net Logon service, which can register and update resource records used by Active Directory domain controllers.

Record update

When a DNS dynamic update is processed for a resource record where other characteristics of the record in addition to its time stamp are revised.

Updates generally occur for the following reasons:

  • When a new computer is added to the network and sends an update at startup to register its resource records for the first time with its configured zone.

  • When a computer with existing records in the zone has a change in IP address, causing updates to be sent for its revised name-to-address mappings in DNS zone data.

  • When the Net Logon service registers a new Active Directory domain controller.

Scavenging servers

An optional advanced zone parameter that enables you to specify a restricted list of IP addresses for DNS servers that are enabled to perform scavenging of the zone.

By default, if this parameter is not specified, all Windows 2000 DNS servers enabled to use scavenging that load a directory-integrated zone (also enabled for scavenging) attempt to perform scavenging of the zone. In some cases, this parameter can be useful if it is preferable that scavenging only be performed at some servers loading the directory-integrated zone.

To set this parameter, you must specify the list of IP addresses for the servers enabled to scavenge the zone in the ScavengingServers parameter for the zone. This can be done using the dnscmd command, a command-line based tool for administering Windows DNS servers.

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