OK, I'll try to make this as succinct as possible, but I also want to give all the pertinent details.
Home network, both ethernet and wi-fi. Basically, 4 rooms have CAT6 service which converge on a switch. Right now, the ethernet network is set up with a Mac Mini in one room, an iMac in another room, and the DSL modem (though I'm pretty sure this isn't an internet issue) & wi-fi router (current-gen Airport Extreme) are in a third room. Nothing hooked up to the fourth at this time. This was working well for a while -- the Mac Mini works as a HTPC, so I've been transferring large files, streaming movies/TV shows, etc, to the iMac over the ethernet connection with no difficulties. Meanwhile, the wi-fi has handled everything for the other machines and has done well.
Recently, I am experiencing disconnects from the network on the iMac. I believe this is since 10.8.1, but I can't be sure. In any event, it is definitely in the last couple of weeks or so. If I transfer a file or stream a video from the Mac Mini to the iMac, the ethernet connection will drop. It drops briefly, but periodically/repeatedly. I first noticed this with choppy videos, playing, then stopping for a few moments, then starting up again. Then I noted that my "shared" iTunes Libraries listed in iTunes were disappearing then reappearing in the background. I opened up the Network pane in System Preferences and did a file transfer and watched as it switched from 'connected' to 'not connected' periodically (the 'not connected' status also claims a disconnected cable or that the machine on the other end has ceased responding). The same would happen when streaming video over the same connection.
I did all the usual reboots of all the various hardware components and still had the problem. To narrow down the issue (is it the router, the switch, the modem, the Mac Mini, the iMac?), I started with the easiest to test -- and believe I got my culprit right away.
(1) disconnecting the iMac from the ethernet network and connecting the iMac to the network via wi-fi: no problems at all. Transferring files and streaming from the Mac Mini went great.
(2) transferring files and streaming from the Mac Mini to my MacBook Pro wirelessly went swimmingly.
So - I figure we're looking at (1) the switch; (2) the wiring; or (3) the iMac as the problem -- so:
(3) turning off wi-fi on the MacBook pro, then hooking it up to the ethernet network at the same ethernet port and using the same CAT6 cable that the iMac had been using: everything works great!
These above tests have been repeated several times and the results have been consistent.
So I would think this eliminates the network hardware from the problem -- the MBP used all the same links in the chain that the iMac had and yet we got different results. That makes me believe the issue is software (configuration) or hardware/firmware on the iMac.
I'm a bit of a networking dunce, though, so I haven't done too much on the configuration side except verify that the settings between the iMac and MBP were comparable and they seemed to be. I'm configuring IPv4 via DHCP, and pretty much everything is set for automatic.
Any obvious ideas jump out at anyone? Thanks!!!