A lot of questions here ask how to be able to do this. My question is different, since at least in Windows 10 connecting WiFi and Ethernet just happens on its own, I just ask what does it actually do.
They even have the same range.
In other words, how does the OS decide which connection to use?
3 Answers
Windows sets a metric for interfaces, gateways, and routes to calculate a cost that is associated with using that route. The higher the metric, the higher the cost. This cost will determine the best path to take when sending a packet out on the network.
Considering two or more network interfaces are not disjointed - i.e. they will all get you to the same destinations, then Windows automatically sets a metric based on link speed. And, in Windows 10, connection type.
As an example, if you have both a 1Gbps wired connection and a 802.11AC Wireless connection (connected at a speed of 1.3Gbps) then Windows 10 will choose the following metrics for each interface:
- Wired - Greater than or equal to 200 Mb and less than 2 Gb = 25
- Wireless - Greater than or equal to 500 Mb and less than 2 Gb = 30
In this case, Windows will choose the wired connection.
In previous versions of Windows, each of these connections would've received the same metric, and therefore Windows would've chosen the interface based on binding order in your network configuration. Windows 10 removed the binding order feature, and it's unclear how Windows 10 will respond in the case of having two or more interfaces with the same metric.
If you would prefer to have Windows use a different interface than what it automatically decided on, you can manually change the metric of your gateways, routes, and interfaces.
For more information about the automatic metric feature and the metrics assigned to each interface type, as well as how to change it, see here:
2Windows will prioritize one of the two connections over the other, and use that connection for all traffic until that connection somehow drops, then switches over to the other until that connection somehow drops.
This effectively means, that if the wifi card is prioritized, and it is slower, your network speeds are reduced until it finally switches over.
Its not possible to see or change which adapter is prioritized. It used to be possible in Windows 7, but that trick no longer works. It is advised to disable wifi if you work on LAN too, to ensure that you get the faster speed, unless you don't need the fast speed.
4If the machine is working properly , Wireless should disconnect when you connect a working Ethernet Connection.
Windows will just use one connection - Wired if available and not both.
It uses the Automatic Metric to do this. See the screen shot below taken from the Network and Sharing Center (Control Panel).
If you think your machine is not working properly, that is, set in the default way, you may wish to run the basic repair steps.
Run DISM / SFC to correct small issues. Also make sure Automatic Metric is enabled.
Open cmd.exe with Run as Administrator.
dism.exe /online /cleanup-image /StartComponentCleanup
dism.exe /online /cleanup-image /restorehealth
SFC /SCANNOW
Restart and test.
