Q: Mountain Lion no Wifi after wake from sleep

I was having the same problem.

What i did was in Finder went to /Library/Preferences/SystemConfiguration/  and deleted all the networking plists (refer screen shot). Then restarted the Mac and in Network Preferences reconnected to my WLAN.

That solve the problem. 

I had the same problem...I can't seem to figure out in this thread if you guys have complete wifi problems,internet problems or spinning beachballs...but for me after waking from sleep, my wifi would haven an exclamation mark on the wifi symbol, and I would have to run diagnostics to have internet up and running again. What I did now is manually adjust my DNS(to the value it had been given prior by the DHCP) you can also try 8.8.8.8 or 8.8.4.4 for google DNS.

Now my wifi just connects fine when I wake my macbook from sleep. It seems that the DHCP gives some trouble to automatically provide the DNS somehow since mountain lion....

Wonder if this works for you guys...

Same problems here. I experienced massive packet loss with 10.8+ over WiFi.

Sometimes I could not even connect after awake from sleep, sometimes had very slow connections etc.

Some of the suggestions above somehow changed the effects, but none finally solved it.

I have no Problems with my second MacBook Pro (Lion).

This is how I managed to solve it for me:

My router automatically switched the channel to optimize WiFi experience.

But sometimes Mountain Lion simply did not agree :-) With up to 8 other WiFi networks in my neighborhood, my router often switched to channels that other routers were using too. Everytime my router selected such a channel, my packet loss gained up to 80%. If my router selected a free channel, the problems were gone.

So I switched off automatic channel selection and selected a Channel no other router is using.

Lucky me: All other routers actually use Channels 6 or 11. I selected Channel 1.

So I eliminated automatic channel switching and gained minimum interference by other WiFi networks.

If I revert the router adjustments, the problems are back again.

Switching router channels solved my problems, too. I'm 5 days in, and my many-months dilemma has not reappeared.

What's worked for me is changing computer sleep to "never." Not my preference, but until Apple fixes this, I can live with it.

I also changed my channel, but continued to have a problem until I changed computer sleep to "never."

Thanks. This worked for me

Same problem here. Apple, we need a fix asap!

I have the same problem with my '08 MB.

I finally did a fresh install on a brand new SSD I bought and thought to myself, "This should take care of that darn beachball wifi issues I had every so often after a long sleep".

Nope.

Still happens every so often.

The only solution is to restart.

Luckily this is the "family browser" Mac.

Still frustrating as ****.

Waiting for this to get fixed before upgrading my other Macs.

I've posted on this thread previously that changing  computer sleeo to "never" solved my problem, but since posting that I've noticed that this is not entirely correct. Last night, after being off the computer for seven or so hours, I wasn't initially able to connect to the internet. Eventually, the computer did connect on it's own, but once connected, Safari's pages took forever to load. I didn't bother rebooting before shutting it down for the night.

That's interesting. Would indicate that the bug is in the ML OS and not connected in any way to Lion. So those wiping their hard drive's clean and reinstalling aren't going to rectify this issue either.

A week after a router hard reset and channel changes, I've had no more of the problems I've had since Lion. YMMV.

Haven't tried a router hard reset yet. Can I ask what router you use? I've got an older AEBS and a much newer AX and have wondered if upgrading to a newer AEBS might ectify the problem, but I've read elsewhere that this isn't a hardware issue.

I use a Linksys Cisco E3000, dual band. I changed the channels on both bands, and have had nary a wakeup problem since.

he other day I got a Mac OS X  suggesting a duplicate use of zip address and leading to a renewed DHCP address distinct (although the IP address had been given with a no limit lease and I don't see any reason for whic there could have been a conflict).

Since then, I mus admit the connection looks a bit more stable (but still not decent enough in terms of (in)stability)...