Windows Vista and Windows Server 2008 DNS clients do not honor DNS round robin by default

Article ID: 968920 – Last Review: March 11, 2009 – Revision: 1.0

Windows Vista and Windows Server 2008 DNS clients do not honor DNS round robin by default

Source: Microsoft Support

RAPID PUBLISHING

RAPID PUBLISHING ARTICLES PROVIDE INFORMATION DIRECTLY FROM WITHIN THE MICROSOFT SUPPORT ORGANIZATION. THE INFORMATION CONTAINED HEREIN IS CREATED IN RESPONSE TO EMERGING OR UNIQUE TOPICS, OR IS INTENDED SUPPLEMENT OTHER KNOWLEDGE BASE INFORMATION.

Symptom

By default, Windows Vista and Windows Server 2008 follow RFC 3484 for destination IP address selection, which does not honor DNS round robin. 

Cause

The TCP/IP stack has no reliable way to detect that a destination server is using DNS Round Robin for load balancing. It is up to the server application to have better implementation to achieve reliable load balancing.

Resolution

To resolve this issue, add a registry key that disables subnet prioritization. Add a new registry key with the following settings:

 

HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services Tcpip Parameters

DWORD = OverrideDefaultAddressSelection
Value data: = 1

 

Note: A value of 1 disables subnet prioritization. This is by design for IPv4 and IPv6 in order to comply with RFC 3484

More Information

RFC 3483 Section 6, rule 9 high level explanation, we are following the RFC.

The RFC works well for IPV6 but has the following problem for IPV4 where NATS are popular.

When clients behind NATs use 192.168.X.Y source addresses and follow RFC 3484, servers with the best IP match to this public IP range may become overloaded.

For more information on RFC 3483 visit the following link:

http://www.ietf.org/rfc/rfc3484.txt (http://www.ietf.org/rfc/rfc3484.txt)

Note: This registry option does not exist on Windows Vista pre-SP1 systems.

For Windows Vista and Windows Server 2008, the default value for this registry key is 1.

For Windows 2008 R2 and Windows 7, the default value for this registry key is 0.

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APPLIES TO
  • Windows Vista Business
  • Windows Vista Enterprise
  • Windows Vista Home Premium
  • Windows Vista Home Basic
  • Windows Vista Ultimate
  • Windows Server 2008 Standard
  • Windows Server 2008 Enterprise
  • Windows Server 2008 Datacenter
Keywords: 
kbrapidpub kbnomt KB968920

 

Microsoft Knowledge Base Article

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