Why bridging wireless card and NIC causes problems

[spidey07]

Real quick to get the discussion going. The topic will be about bridging, what it is, what it does and why in most instances bridging a wireless NIC to a wired NIC will reak havoc and create the dredded, network crippling "bridge loop". Also incorrectly called a "spanning-tree loop". Spanning-tree seeks to stop this behavior and does a nice job of it. But what if your switch doesn't run spanning-tree like so many/most "dumb" switches do?

Well you're kinda screwed. This thread will be devoted to explaining what happens, why it happens and what to look for.

 

[imagoon]

My most interesting experience:

When bridged (the guy who had the laptop would stop doing this either...) he would come in to the office where the wireless and the wired shared the same IP range. It would result in the DHCP server filling up with "BAD_IP_ADDRESS" entries because both adapters would request an IP. DHCP servers (windows at least) will verify that an IP doesn't respond before it hands it out. It would then see it's own request loop through the wireless bridge and look like it is generating traffic. It would then mark the IP address bad and try another. Bringing network to a crawl (from the looping data packets and later by exhausting the IP scope so no other machines could get in afterward.

What we would see: Basically the activity lights on the switch(s) would more or less go solid on. Even a heavily loaded "normal" switch will rarely just lock the activity light on.

Next hint is everyone saying the network is slow or server not reachable errors.

Connecting the test laptop would result in a "scope exhausted" message in the event log.

Running wireshark would show tons and tons or error frames, runts, collisions and misc other.

 

[drebo]

We cut a guy's hand off for this.