How does Windows decides which DNS Server to use when resolving names?

Question

What algorithm does Windows use to decide which DNS Server it will query in order to resolve names?

Let's say I have several interfaces, all active, some with no dns server specified, some told to determine it automatically, and some with it specified manually (in interface ipv4 AND interface ipv6).

I'm asking for an answer to this general question hoping that I know how to solve a more specific problem in Windows Vista - I have two interfaces, one a lower metric and a DNS server specified manually. nslookup uses THIS DNS server and resolves the names correctly. However, all other applications fail to resolve the name unless I manually specify a DNS server for the other interface, which the applications then use. nslookup also uses the DNS server specified for this other interface once it is specified.

Thanks

Answer 1

If I'm not mistaken, it's determined by the NIC binding order in the Advanced Settings in the network connections folder. You can verify it by changing the binding order of the various NIC's and running nslookup as a test.

To expand on my answer, citing the article that Evan linked, here is an excerpt from said article:

The DNS Client service queries the DNS servers in the following order:

1. The DNS Client service sends the name query to the first DNS server on the preferred adapter’s list of DNS servers and waits one second for a response.

2. If the DNS Client service does not receive a response from the first DNS server within one second, it sends the name query to the first DNS servers on all adapters that are still under consideration and waits two seconds for a response.

3. If the DNS Client service does not receive a response from any DNS server within two seconds, the DNS Client service sends the query to all DNS servers on all adapters that are still under consideration and waits another two seconds for a response.

4. If the DNS Client service still does not receive a response from any DNS server, it sends the name query to all DNS servers on all adapters that are still under consideration and waits four seconds for a response.

5. If it the DNS Client service does not receive a response from any DNS server, the DNS client sends the query to all DNS servers on all adapters that are still under consideration and waits eight seconds for a response.

The preferred adapter in step 1 being the adapter that's listed first in the binding order.

Answer 2

In Windows 10 (and Windows Server 2016) you must update the metric of each interface in the order you want.

1. Goto Control Panel > Network and Internet > Network Connections
2. Right click the desired connection (Higher Priority Connection)
3. Click Properties > Internet Protocol Version 4
4. Click Properties > Advanced
5. Uncheck 'Automatic Metric'
6. Enter 10 in 'Interface Metric'
7. Click OK

References:

• answers.microsoft.com
• Configure the Order of Network Interfaces - Microsoft Docs

I used 10 for my LAN, 20 for WLAN, and 100 for VPN Interfaces (I prefer local DNS at work, this may be reverse for others). Remember lower metric = higher priority.

See this article in Microsoft Support for An explanation of the Automatic Metric feature for IPv4 routes.

Answer 3

This page describes the algorithm used by Windows to perform DNS queries. It's not in depth enough to give you all the answers you're looking for, but some time w/ a sniffer and this article ought to be all you need to determine what's happening in your specific situation.

Answer 4

I had exactly the same problem. I've spent a day trying to figure it out. Now I know and it works like a charm.

If you have several network cards and if if specify DNS server in each of them. Do you know what DNS server will be used at last?

Well you can check it via practice.

nslookup 192.168.3.6

So you see the server that your PC actually use

The question is - From what depends what DNS server windows choose to use and how we can change it.

We especially need it when we use VPN clients.

The answer from qwerty2010 is right and correct. But you can use it ONLY when you have NIC in control panel - network and sharing center - change adapter settings - list of nics

Only if you see the nic that is reponsible for your VPN client you can use graphical way to point windows what dns server (that is specified on a particular nic) you'd like to use.

So you go Network and sharing centre -> Change adapter settings -> Advanced -> Advanced settings -> and you move UP the nic with DNS you'd like to USE. (UP you need to lift it UP).

However if for instance you use Shrew vpn client - you will not have any nics.

What do you do.

You open registry.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}

And you look in subfolders 0000, 0001 etc the folder with

DriverDesc = Shrew Soft Virtual Adapter

fine. Then you copy to the clipboard

NetCfgInstanceId = {B498E7DE-7257-48F6-AD32-60E470030F05}

Now you go

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Linkage]

and you open key = Bind. You'll see the list like this

\Device\{1DF89CE3-CAAD-4EB7-A53F-AD16BC1D5EFD}
\Device\{70126DBE-B44D-4392-9417-0CABD6E384B1}
\Device\{D5127F8E-E7BB-4661-AE5A-A922614173D0}
\Device\{C44039AB-6801-4A9B-A736-3B12782FF411}
\Device\{85231D0F-CD05-4774-A983-632C5D83AC62}
\Device\{7E87BC81-8C58-4E05-9FA0-7897A6AA5CCE}
\Device\{3A1A3EFC-A9DE-4BCA-BAF6-81C7074487E0}
\Device\{8D41EDFC-04AC-4537-B5D5-0D54EB51A023}

All you have to do is put to the top

\Device\{B498E7DE-7257-48F6-AD32-60E470030F05}
\Device\{1DF89CE3-CAAD-4EB7-A53F-AD16BC1D5EFD}
\Device\{70126DBE-B44D-4392-9417-0CABD6E384B1}
\Device\{D5127F8E-E7BB-4661-AE5A-A922614173D0}
\Device\{C44039AB-6801-4A9B-A736-3B12782FF411}
\Device\{85231D0F-CD05-4774-A983-632C5D83AC62}
\Device\{7E87BC81-8C58-4E05-9FA0-7897A6AA5CCE}
\Device\{3A1A3EFC-A9DE-4BCA-BAF6-81C7074487E0}
\Device\{8D41EDFC-04AC-4537-B5D5-0D54EB51A023}

That's all. There is no need to reboot.

Now your windows will use DNS specified in shrew vpn nic when you use vpn connection.

Answer 5

As this might help you or others, you can disable the windows round-robin usage of the listed dns to make the dns usage more predictable. Try setting the RoundRobin=0 in the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DNS\Parameters (reference) to disable the dns round-robing.

There is also a "timeout" for rotating the servers, you can also try to setting it to zero:

 HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters
 ServerPriorityTimeLimit=0

Answer 6

It doesn't decide randomly. You're connected to a router which gets it IP from a company which has DNS servers. They get your request unless you alter the IP manually to another DNS, for instance: OpenDns. Or perhaps you decide on having your own DNS servers. That works too. Just enter the IP adresses in the network center and all should be well. And yes, you'll have to set those manually.

You can also adjust a file in C:\Windows\System32 called "hosts" with no extension. It allows you to have URL-requests redirected instead of being sent to the standard DNS. To a local server(which must be running and listening to port 80)