With both wired and wireless network connection, prefer to go wired, but metric doesn’t always work.

95 pts.
Microsoft Windows 7
Wireless network management
Wireless networking
When a laptop has both wireless and wired connection at the same time, we want to make sure the network traffic is going through the ethernet cable first instead of going via air. A lot of research was telling me that Windows has the preferred route to higher throughput interface. I found this to be true on Windows 7 that it assigned metric 10 on the wired connection and metric 25 on wireless. Here is the problem. When I have both network connection on and start transfer files from a server, in Task Manager networking tab I can see the traffic is going through the wired connection as expected. However, if the laptop is "on wireless first" without network cable, then connection to a server, say Server1, is initialed, Windows 7 seems memorize this path or route. Later after the ethernet cable is plugged in, the traffic going to Server1 will be still on wireless interface rather than the wired connection. Looks like metric is not playing the magic any more once there is cache in the system. On the other hand, with both connection on, if I try to connect to another server, the wired connection will be taken. To me, the metric only works for the first time connection. Any thought to correct the problem and make ethernet connection always be the preferred route?

Answer Wiki

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When adding a second connection (i.e. a wireless connnected system adding a wired LAN connect) the client system should determine costing of both routes to the destination over each NIC to determine which NIC to send traffic out. This is all based off of the TOTAL routing costs of each route to the destination and not just the local interface metric.

So what you are most likely seeing is the wireless route has a similar or lower total routing cost as the wired route to the resources which you are connecting. One item you can do to trigger a route change is to set the route costs at the router port for the wireless LAN to a higher number than the wired routes. As an example, set the wired routes to a metric of between 1-4 as you need and set wireless routes metrics to between 10-15 as needed. This should drive most traffic to choose the wired route over a wireless route. You will need to diagram out routes to resources and the costing of each router hop to determine flows.

NOTE 1: The default routing metric on the Windows client is the automatic metric. The automatic metric is based off of reported network speed of the NIC.

NOTE 2: I have seen where the wireless NIC driver will initially (and erroneously) report that the connection has the maximum theoretical speed generating a very low metric which is never updated. Update your NIC driver first then if not resolved open a case with your vendor for an updated driver to resolve.

An explanation of the Automatic Metric feature for Internet Protocol routes.

TCP/IP Routing Basics for Windows NT.

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  • jinteik
    from what i know is also when you are connected using wired, ur wireless will be turn off..i guess the system / how they program it to use wired is more stable / better than wireless
    18,995 pointsBadges:
  • springman
    Thank you for the great insight on routing cost. I've never thought of that. The network equipment involved to this issue is only one core switch (layer 3 as the default gateway) and one edge switch (layter 2). There is no physical router presents for the issue. The routing occurs on the core switch and all on the VLAN'ng. All VLANs have the same routing metric (cost) on 1. Looks like I need to figure out if there is a way to change the metric/cost/distance setting.
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