Smart multi-homed name resolution is a DNS related feature that Microsoft introduced in Windows 8 and implemented in Windows 10 as well.
The feature is designed to speed up DNS resolution on a device running Windows 8 or newer by sending DNS requests across all available network adapters. Microsoft refined the feature in Windows 10 as it selects the information that is returned the fastest automatically.
While the feature makes sense from a performance point of view, it introduces an issue from a privacy one.
If you connect to a VPN network on a Windows machine for instance, smart multi-homed name resolution may lead to DNS leakage. Since requests are sent out to all network adapters at the same time, all configured DNS servers receive the requests and with them information on the sites that you visit.
Microsoft introduced a Registry key and policy to manage the feature in Windows 8.
Note: manipulating the Registry may lead to issues if done incorrectly. It is suggested that you create a backup of the Windows Registry before you continue. This can be done by selecting a Registry Hive in the Registry Editor, and then File > Export from the menu bar.
I have created a Registry file that makes both changes to the Windows Registry when executed. You can download it with a click on the following link: disable-smart-name-resolution.zip
The Registry key that worked under Windows 8 does not seem to work under Windows 10 anymore. Windows 10 users and admins may set a policy however to turn the feature off.
Specifies that a multi-homed DNS client should optimize name resolution across networks. The setting improves performance by issuing parallel DNS, link local multicast name resolution (LLMNR) and NetBIOS over TCP/IP (NetBT) queries across all networks. In the event that multiple positive responses are received, the network binding order is used to determine which response to accept.
Note that the Group Policy Editor is only available in professional editions of Windows 10. Windows 10 Home users may want to check out Policy Plus that introduces policy editing to Home editions of Windows 10.
If you enable this policy setting, the DNS client will not perform any optimizations. DNS queries will be issued across all networks first. LLMNR queries will be issued if the DNS queries fail, followed by NetBT queries if LLMNR queries fail.
Some DNS clients that you may run on Windows machines come with DNS leak protection to prevent these leaks. OpenDNS users may enable the block-outside-dns option for instance in the client to do so.
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Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.