I had some trouble with my iMac today. For no apparent reason, my internet connection seemed to slow down. A speed test on http://testmy.net reported only 1 Mbps, rather than the 10 Mbps that Comcast usually provides. I did all the usual simple things: reset the router and cable modem, reboot the iMac. No improvement. OK, now on to the Mac voodoo: reset the PRAM (reboot holding cmd-opt-P-R), reset the SMC (unplug everything and hold the power button for 10 seconds), delete and replace the network locations. Still no good. Actually it got worse, my Mac said nothing was connected to the ethernet port. Could be a router problem? Maybe, but the same cable worked fine with a MacBook so the problem had to be with the iMac. A safe boot (holding shift) got me back to only a 1 Mbps connection on my admin account. I googled for more clues. Found a few useful looking web pages, but no definitive answer. https://discussions.apple.com/docs/DOC-3353 https://discussions.apple.com/docs/DOC-3421 http://support.apple.com/kb/HT1714 Along the way, I saw someone mention the commands to turn off the ethernet port and turn it back on again: % sudo ifconfig en0 down % sudo ifconfig en0 up That seemed to help. Of course, I did a lot of fiddling so I can't be sure exactly what fixed the problem, but I thought I'd mention ifconfig here just in case someone else runs into a similar problem. I feel lucky to be back to normal. Now, back to work.