Disabling Multicast Advertising on OSX
The problem
OSX has an interesting feature whereby it effectively takes on the IP address of other Macs, for the purpose of forwarding certain network broadcasts on their behalf.Unfortunately, this behaviour sets off alarms in our network monitoring systems, and can also confuse our maintenance automation and network infrastructure security. As such, it's something we require users to disable when connected to the CSE network.
The solution
Disabling multicast advertising requires editing a configuration file on your computer. As manually editing configuration files can potentially disable your machine if you make a mistake, it's important that you back up your Mac before continuing.The file you need to edit is /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist.
So, open up a terminal and type:
sudo nano /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
Scroll down to the ProgramArguments section, and add the line <string>-NoMulticastAdvertisements<string>:
<key>ProgramArguments</key>
<array>
<string>/usr/sbin/mDNSResponder</string>
<string>-launchd</string>
<string>-NoMulticastAdvertisements</string>
</array>
Save and exit. If you used emacs to edit instead, it's important that you remove the auto-backup file com.apple.mDNSResponder.plist~ that emacs creates, or your Mac will not restart correctly. Restart your mac, and your friendly sysadmins will thank you for making their lives easier.
OR, download a little app to do the above here
An alternate solution
The Internet Sharing feature uses something called Bonjour Sleep Proxy, which causes a computer running OSX to take over other computers' IP addresses when they go to sleep. More about it can be read at this Wikipedia article.You can turn off Internet Sharing by going to System Preferences -> Sharing -> Internet Sharing and making sure everything is unticked. This should stop the alarms on our network from being set off due to IP address changes.