[DaveJ]

A few weeks ago my iMac 10.6.8 began experiencing dropped and slow connections to the internet -- there are stretches when the connectivity is fine, then it will disappear, eventually return, and be fine for a while. Affects browsers, mail, iTunes. Power cycling Airport will resurrect the connectivity immediately. I have Little Snitch and can watch network activity. When the connectivity is lost -- it's lost. There is nothing being up- or downloaded.

It's clearly the iMac at fault because none of the other computers on the network has problems. I can download video to my iPad sitting at the iMac faster than the iMac can -- or indeed when the iMac is not connected at all, so interference seems unlikely. Bizarrely, the problem doesn't seem to affect the LAN: AirTunes works fine, the network drive works fine, the remote printer works fine. Says to me (plus that the other computers work) that's not the BaseStation.

I really don't want to do a clean re-install for obvious reasons or upgrade to Lion since my aging Creative Suite will have issues I hear.

I've followed lots of suggestions including repeatedly repairing preferences, zapping the PRAM, deleting com.apple.alf.plist (and a couple other system files that I don't remember). The router assigns a static IP to the iMac. That doesn't help either.

Suggestions?

Thanks in advance.

Any suggestions?

[Thorzdad]

Originally Posted by DaveJ 

The router assigns a static IP to the iMac.

Why is it doing this? All devices should be sharing a single IP from the router.
You don't say, but I assume you've made sure there isn't a DNS mis-match between the iMac and the router?

[Spheric Harlot]

FWIW, I've had sporadic internet dropouts on my Thunderbolt 13" MacBook Pro, and it turned out to be a faulty network controller. New main logic board, all is well.

[Cold Warrior]

If you're on wifi, have you tried changing the airport router's channel?

On your iMac hold the option key and click the airport icon in your menu bar.

Mouse over each entry and it will pop up text showing channel. Make a mental note of what you see.

In airport utility, change the channel to some other one besides what you saw. Ideally pick a channel two channels removed from any others. E.g., if you saw wifi points on channels 6 and 11, pick 1-4 or 8/9.