DNS Dynamic Update
- How Windows 2000 Computers Update their DNS Names
- Example: How Dynamic Update Works
- Secure Dynamic Update
This article discusses dynamic update, which enables DNS client computers to register and dynamically update their resource records with a DNS server whenever changes occur. This updating reduces the need for manual administration of zone records, especially for clients that frequently move or change locations, and use DHCP to obtain an IP address.
Paul T. Ammann is the author of several books on computing and networking. This article is excerpted from his book IP Solutions for Windows 2000 (Prentice Hall PTR, 2001, ISBN 0-13-091170-4).
Windows 2000 provides client and server support for use of dynamic updates, as described in RFC 2136. For DNS servers, the DNS service allows dynamic update to be enabled or disabled on a per-zone basis at each server configured to load either a standard primary or directory-integrated zone. By default, client computers running under any version of Windows 2000 dynamically update their host (A) resource records (RRs) in DNS when configured for TCP/IP.
How Windows 2000 Computers Update their DNS Names
By default, computers that run Windows 2000 and are statically configured for TCP/IP attempt to dynamically register host (A) and pointer (PTR) resource records (RRs) for IP addresses configured and used by their installed network connections. By default, all computers register records based on their full computer name.
For Windows 2000 computers, the primary full computer name, a fully qualified domain name (FQDN), is based on the following system settings: The Primary DNS suffix of this computer appended to the Computer name.
Both of these settings are displayed or configured from the Network Identification tab in System properties.
Dynamic updates can be sent for any of the following reasons or events:
An IP address is added, removed, or modified in the TCP/IP properties configuration for any one of the installed network connections.
An IP address lease changes or renews with the DHCP server any one of the installed network connections (for example, when the computer is started or if the ipconfig/renew command is used).
The ipconfig/registerdns command is used to manually force a refresh of the client name registration in DNS.
Startup time, when the computer is turned on.
When one of the previous events triggers a dynamic update, the DHCP Client service (not the DNS Client service) sends updates. This is designed so that if a change to the IP address information occurs because of DHCP, corresponding updates in DNS are performed to synchronize name-to-address mappings for the computer. The DHCP Client service performs this function for all network connections used on the system, including connections not configured to use DHCP.
The process of the way dynamic updates are performed for Windows 2000 computers that use DHCP to obtain their IP address is different from what is described in this section.
The update process described in this section assumes that Windows 2000 installation defaults are in effect. Specific names and update behavior is tunable where advanced TCP/IP properties are configured to use non-default DNS settings.
In addition to the full computer name (or primary name) of the computer, additional connection-specific DNS names can be configured and optionally registered or updated in DNS.