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maybe someone can assist a beginner to solve a problem. I have set up mobile broadband and wired network in the network manager in Ubuntu 11.04. Yet, they won't work at the same time. Wired network seems to have priority and is connected at start up. To get the mobile broadband connection running I have to manually delete the wired network from nm every time. The other way around I can get the wired network running by disabling mobile broadband. I tried to fix things by manually configuring the wired network, but it didn't help.

NM in Ubuntu seems to see these two connections as two different networks and doesn't accept them running at the same time. In Windows 7 as well as in XP the same combination works without any problems.

Any idea how to fix this problem? Maybe by handling mobile broadband through wvdial and wired network through NM? This may be a workaround, but I'd prefer to handle both connections through NM.

Any help is very appreciated.

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2 Answers 2

You are right in that they are two separate networks. The way OS's handle this is through prioritising to ensure that one is always used unless unavailable, at which time the OS will use the other one.

You can understand why they can't both be used as one network if you try and imagine where packets should route - the TCP/IP stack on a port knows that if it receives a packet for an established session it should match up with one sent out that port earlier. If it can't match it, the only sensible option is to drop the packet.

You can use them separately to route, though - so you could set them up so the wired network routes all packets to the Internet and the wireless one routes all packets to local machines - but the destination networks must be exclusive to each other.

Wired networks almost always get highest priority, as they are usually fastest and most reliable - and it sounds like your system is working correctly.

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Ubuntu Network Manager might not be a good choice for you. Because it wont handle multiple networks at the same time. Try other network managers instead. Like WCID http://www.wicd.net/ this network manager is more powerful than the Ubuntu Network Manager. But it became a quite a big hassle for me to install it. It should be worth the try for you. But at the moment i'm not using it.

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