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We're seeing some very strange behavior on one of our LANs, I'm hoping someone might recognize what it is.

The LAN consists of several Linux boxes and several MacOS/X boxes, all connected by 100MBps Ethernet through a switch. It's not connected to the Internet.

What we've found is that when we put one of the MacOS/X boxes (a Mac Pro) to sleep (via the the "Sleep" menu item in the Apple menu), the LAN stops working for about 10 seconds. We see this in the applications we are running, and also we set up "ping" processes from and to various of the other machines and we can see the ping times go way up (to the 2000-8000 millisecond range!) during this 10 second period.

After 10 seconds, the network seems to recover and work again. As a test, we tried just disconnecting the Mac Pro's Ethernet cable (without putting the Mac to sleep), and that had no effect on the LAN... it's only when the Mac goes to sleep that trouble occurs.

Any thoughts on what might be wrong, or how to figure this out?

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sleep the mac then disconnect it from the lan, what happens? – tony roth Jul 1 '10 at 18:14

Run a traceroute on one of the other machines and make sure it's not somehow being routed through your Mac Pro. That would be bizarre, but hey, easy to check.

After that, I'd check to see if it's trying to sync something to the network before it shuts down. Start up ipTraf on one of the Linux boxes and see if it's getting any weird traffic.

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