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June 15, 2007


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We recently discovered this on our network as well.

It scares us greatly, as we are a 24/7 mission critical shop. The network MUST work. 22% of our 700+ clients are wireless.

Not to mention being in a public service industry. So 'can you please turn that off?' isn't gonna cut it.

Several years ago, i saw some Macs doing multicast on our network too. The multicast traffic was killing some Linksys gear and causing general havoc on the network. We've since removed just about all "Best Buy" class gear and haven't seen any additional problems.

I'm interested to see what you discover.

Regarding Macs and Multicast, all Macs from 10.2 forward include MulticastDNS (UDP for zero configuration service discovery, AKA Bonjour or Rendezvous. To see what machines are available use a tool like Bonjour Browser (http://www.tildesoft.com/Programs.html)

For more info on see:

The inevitable question - How to disable it:
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

The -w makes the change permanent.

Try this to reenable it.
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

Note that Bonjour is pervasive on the Mac and is used by many different programs to discover what's available on the network. I'd recommend against disabling Bonjour and instead limit what is being broadcast by turning off services that are not needed in System Preferences, Sharing.

You might also have success by disabling multicast in your WAPs, provided that they have that option.


Your bluetooth discovery actually makes sense to me now. I had just recently noticed that when I have my bluetooth usb adapter plugged in, that I experienced connection drops on my G wireless link. Never researching this, I would not have thought bluetooth and 802.11g would collide as much as they do. Duh. :)

Thanks man. This makes me want to turn off my Treo's bluetooth when I'm not using it. ;)

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  • Jason Powell is the Information Technology Director at Granger Community Church. The views and opinions expressed here are not necessarily those of GCC ...
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