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I am asking myself for quite some time this question.

With a normal laptop you can have at least two internet connections: ethernet (wired LAN) and wifi (wireless). If you use a USB cellular modem (GPRS, 3G or LTS) you can add one more connection.

The difference between ethernet and the wireless connections is the available bandwidth. And the cellular internet connection has in most cases some kind of cost associated.

So, how does Linux decide which connection to use for the internet traffic?

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  • more specifically, I believe you want to know how "network manager" decides which connection to use. – mchid Mar 22 '15 at 4:00
  • on my laptop, network-manager always uses eht0 over wlan0. – mchid Mar 22 '15 at 4:02
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I think it uses the last one that was connected...

And uses different routes (route / iptables) to decide where to send internet traffic.

In case you wanted to have 2 connections at the same time, but choose which one to use for internet traffic I know there are ways to choose between them. Luckily you didn't ask how because I don't remember at the moment... I think it's changing the default gateway to use one or the other, but a web search should find out for sure.

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AFAIK, most distributions of Linux, along with most Windows versions, should automatically use the connection with the highest speed, unless the user has something specific configured.

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