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So, this just happened. I just took down an entire corporate network with bridged adaptors in Windows 8.

Let's back up.

Last night, I was preparing for my talks at CodeMash. When I give Xbox development talks, I have to use a strange network configuration. You see, to debug on an Xbox, you have to have an active connection to both Xbox Live and the development machine. The easiest way to do this on isolated conference wifi is to bridge the wireless connection to the wired connection of my laptop while using a cross-over cable to the Xbox.

However, this was the first time I've had to do it with Windows 8. So, I tested it all out last night and got it working. Thinking like any other laptop I've had, I left the connections bridged. Let's face it, on Win7 when you accidently duel inputted bridged connections, nothing really happens.

Let's back up.

I came to my attention a few days ago that the only machine I had capable of running Hyper-V was my laptop. My home laptop is a Pentium, and my work desktop is a Core Duo. Thus, all my phone development has to be done on the i5 work laptop. Due to this, I set up a docking station for my laptop so I could use better stuff while in the office. During this time, I pulled a network cable into the docking station.

Fast forward to this morning. I'm doing my usual work stuff. At some point, I put the laptop in the docking station. 10 to 20 minutes later, the entire corporate network goes tango uniform.

The network gnomes go into a furious round of creating ulcers that would make any doctor's eyes turn to dollar signs. BCBS and Tricare felt a disturbance in the force. Smurf just got real.

Four hours later, they managed to fix the network, but don't know what happened or how it was fixed. Hi-five were about, and many an M&M gave its life in the victory feast. There was just one nagging problem. The thing that worked shouldn't have worked.

The chief network gnome started trying to isolate the problem. In the process, he isolated one of the networks switches to pull it completely off the network. As soon as he did this, everything came back to life.

The problem being that the switch without a connection to the network was not only still connected, it was completely up and operational with the rest of the network. The only way this could have happened was if, somewhere on that switch, there was another router that had mysteriously been connected.

At this point, I raised both hands, triumphantly, and announced "IT WAS ME!" You see, any fool can take out a computer, it takes a programmer to take out an entire network.

The network connection in my office goes to a little four port switch. That connection goes to a few devices in my office. The other side goes to the isolated network switch. The adaptor for the corporate wifi goes to a different one of the switch. My laptop became the network gateway for the isolated switch.

Here is the moral of the story. Windows 8 does some thing new and unique when creating bridged connections. I creates a new adaptor called the "Network Bridge." This network bridge is a software router. It then connects the two bridged connections, using the one as a gateway for the other. However, in this case, this software router is a full blown router, DHCP server and all. Thus, my laptop created a HUGE feedback loop in the network. When we isolated the connection, it became the gateway for a large portion of the corporate office. We unplugged the network cable from the back of the docking station, and everything when back to normal.

I have not, yet, seen this documented in such a way. As such, I hope us figuring out this new way of bridging connections in Windows 8 can keep you ulcer free, doctors clear-eyed, and health insurance companies coming for you in a manner similar to the Empire.

Posted on Thursday, January 3, 2013 3:49 PM Win8 | Back to top

Comments on this post: Bridged Adaptors in Windows 8

# re: Bridged Adaptors in Windows 8
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Yeap. In Win7 it was easy to share network connection to Xbox via bridging LAN & WLAN connections from a laptop. 100% impossible now in Windows 8 (actually 8.1 atm). It creates the bridge, shows ethernet cable (to XBOX) connected -> everything worked like this in Win7. Win8, with all media streaming etc options enabled -> no go.
Left by Artifex 28 on Oct 23, 2013 9:32 AM

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