Extension Mechanisms for DNS (EDNS) are optional protocol elements that can be included in communications between DNS requestors and DNS responders. EDNS0 refers to the first RFC for EDNS (RFC 2671), which permits DNS requestors to advertise the size of their UDP packets and facilitates the transfer of packets larger than 512 octets. For more information about EDNS0, see Using Extension Mechanisms for DNS (EDNS0).
EDNS0 is enabled by default in Windows Server® 2008 R2 In previous versions of Windows, it was necessary to enable EDNS0 manually using the command line or the Windows Registry.
This feature will be of interest to IT professionals who manage Active Directory® Domain Services (AD DS) and DNS.
The registry key EnableEDNSProbes is set to 1 in Windows Server 2008 R2. This setting enables EDNS0. In previous versions of Windows, this registry key was set to a value of 0, which disables EDNS0.