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I have a Samsung NC-10 netbook which I take to work every day. Most of the time I use it just on the train/bus, but I also use it at work and home.

It has a built-in 3G card which I want to use when travelling, but I'd prefer to use wifi when I'm at work or home, for obvious reasons. Unfortunately, if the 3G connection is up, Windows appears to use that in preference to wifi.

Starting up and shutting down the 3G modem is a bit of a pain - it's not hard as such, just a bit inconvenient. Ideally I'd like it to always be up, and even have the connection itself up all the time, but without routing traffic through it if there's a wifi connection up. This is what my Android phone does, for example.

Is there somewhere in Windows which lets me express an ordering for network interfaces? I suspect the routing table may be relevant, but it's a bit of a pain to mess around with. I'd really expect there to be a simple GUI way of setting this up - after all, it would equally be useful when dealing with wired vs wifi connections.

I'm currently using Windows XP Home, but Windows 7 answers would also be useful as I'll be migrating soon.

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I hope one day we can use SCTP (or something similar). Imagine transparent failover. Connections could survive switching from wifi to 3g and vice versa. –  Tarnay Kálmán Mar 28 '11 at 10:48
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5 Answers

up vote 16 down vote accepted

You need to change the metric of the routes for the adapter. If you do 'route print' at a command prompt you should see the metrics for the various routes for your adapters. The route with the lowest metric will get used first when sending out traffic.

If you go into the networking control panel and into the TCP/IP settings for your wifi adapter and then to advanced their should be an option called 'Automatic Metric' you need turn this off and asign a metric yourself. Just set it lower than your 3G adapters metric

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It's a little bit dodgy because the metric for the 3G card is 1, and that's the lowest I can set the wifi adapter to - but it seems to be working, so I'll accept this answer :) If you know how to change the metric for the 3G card as well, that would be even better... –  Jon Skeet Jul 15 '09 at 9:29
    
Hmm... today it seems to be using 3G in preference... both interfaces having metric 1 is a pain :( –  Jon Skeet Jul 16 '09 at 10:14
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Can't you change (increase) the metric of the 3G interface in the same way? This will "make space" for the wifi connection's metric to be lower. –  tomfanning Jul 17 '09 at 13:05
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In Windows Vista:

  • Open Network and Sharing Center
  • Manage network connections
  • Alt-N S (Advanced -> Advanced Settings)

You can change the provider order in here, however I am not sure if it affects routing to be honest. The other option would be to bridge the two connections, but then you don't have control of which connection is being used.

I did this on my Acer when I didn't have ADSL and only 3G and it worked, but there is no fine grained control I am aware of.

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Hmm - it's slightly different in XP: Control Panel -> Network Connections -> Advanced menu -> Advanced Settings... but it's there! Unfortunately, the 3G card isn't listed and "Remote Access Connections" is already at the bottom of the list. Looks like the right dialog though, so will play further. –  Jon Skeet Jul 15 '09 at 9:10
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How to change the binding order of network adapters in Windows XP and in Windows 2000 (http://support.microsoft.com/kb/894564)

It's useful also when you want to decide weather your VPN connection should be the first or not.

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In Windows Vista/7, run "ncpa.cpl" In Windows XP, just goto Control Panel and open Network Connections.

The Network Connections window has an Advanced menu, select the Advanced Settings entry.

The Advanced Settings dialog box's Adapters and Bindings tab will show the order for preference in the Connections list box. move the wireless connection above the 3G or [Remote Access connections] entry.

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Unfortunately the "Remote Access connections" entry is already at the bottom, so I don't know why it's using it... –  Jon Skeet Jul 15 '09 at 9:12
    
You should call that the "Internet properties". You can access that via the Tools menu from IE, but it's also in control panel, and can be opened from the "Change proxy settings" button in the "Under the hood" tabe of Google Chrome Options. Other browsers will probably also have ways to open the "Internet properties". :) –  Bernhard Hofmann Jul 15 '09 at 9:16
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First of all, to view your order of interfaces by the os, run "route print' on the command prompt.

The metric value displayed determines which interface comes first in ascending order. For your LAN connection to be chosen over a 3G connection on an XP machine, just go to your LAN interface properties, in the connection tab, choose "Internet Protocol (TCP/IP)" and click "Properties", instead of changing your IP address, click the "Advanced" button and at the bottom, uncheck "Automatic metric" then make the interface metric value "1".

You can leave the rest of the interfaces stay with auto metric. Apply changes to your LAN interface and that will resolve your issue.

Be careful as applying the changes refreshes your LAN connection.

Regards,

Chris Musasizi

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