Q: Installed Lion, now cannot connect to internet!!!

My issue is solved.Ended up being the firewall in Lion. Was on the phone with Apple support for 2 hours last night and they couldn't nail it. I ended up finding some helpful information in this thread this morning.

https://discussions.apple.com/thread/3189562?start=15&tstart=0

Specifically a post from wifiguru:

Turn off firewall first.

octamm, try this:

Backup this file in /Library/Preferences and the delete it.

Command 1:

sudo mv  /Library/Preferences/com.apple.alf.plist  /Library/Preferences/com.apple.alf.plist.orig

Command 2

sudo rm  /Library/Preferences/com.apple.alf.plist

Now reboot your machine and then turn the firewall ON after a reboot. Then reboot a couple times and test if everything works.

This worked for me. In the end it was the Lion firewall blocking my iMac from getting an IP address from my router. Disabling it immediately solved the issue. Turning it back on after reboot still disabled all connections. After running those commands in terminal and restarting and re-enabling I am now back to work this morning.

Hopefully this can help someone else and save the frustrations I was having yesterday. Best!

Same problem here ... wireless worked fine, but my main desktop "wired" computer didn't work.  aaron260 suggestion of moving System Configuration to the desktop and rebooting worked for me ...

So in my continued putzing my router sees the computer and all the settings match. I went and tried to reinstall ln through the restart while holding down option. It didn't really want to reels load lion but going to apple support worked, I could browse the web from there.  I restarted normal and still no Internet.

I concur. I had same issues of most internet-related apps not working (though Mail did) but once I uninstalled Avast everything worked.

you should be able to delete that system configuration folder from the desktop.  When you restart the computer the OS recreates that folder into the place you originally moved it from, with all default settings as well. 

To all with this problem, this is what I have gleaned - enough to determine that Apple actually does have a serious problem here.

Specs:

• brand new 17" MBP early 2011 model
• wifi running from time capsule connected by Ethernet to dsl modem
• all connections dhcp configured
• I run no AV or firewall utilities, so no Avast to blame ;-)

The existing connection and hardware worked perfectly to download Lion from the mac app store.

After installing Lion DHCP and DNS will not work: evidence and remedial attempts are listed below...

• When checking network settings a random, self generated ip address was being used.
• Renewing dhcp lease fails, so I specified ip settings manually, including dns servers
• I used the local router for dns before but added google dns, open dns and a couple of other dns servers to the list of dns servers using the network settings panel.
• I used the network utility to test connections - pinging ip addresses works fine but pinging a web address fails as dns fails to resolve. Pinging the router and other ip addresses on the local wifi also works - but local device names are also unresolvable (only from Lion - the other devices all resolve just fine).
• iPad, iPhone and a second, older MBP connect to the same network with no issues
• Rebooting Lion makes no difference
• Oddly skype connects (and can carry out an IM chat) but app store, safari, chrome, firefox - all dns based software fails
• Creating new locations / new connections with the network connection wizard fails
• Apple's own network diagnostics reports that the machine is not connected to the Internet (despite success with pinging net addresses directly) - a further indication that the problem lies with DNS
• All airport devices are not seen or recognised - airport utility tells me that no airport devices are available.

This IS a software issue because rebooting to recovery mode, oddly enough, finds the 'Search help' option able to connect using safari with the same hardware and no additional changes.

Let me repeat that: Recovery mode (booting with cmd-R) successfully connects to the same unavailable Internet with no hardware or software changes.

The only difference is that the full blown version of Lion is not loaded and running.

In recovery mode I am able to connect to the time machine and do a viable restore of Snow Leopard, after which the system boots and all comms (Airport, Ethernet) work 100% (it is from the restored system that I am typing this message).

At no stage did rebooting the time capsule or router make any difference (I methodically tried variations of this process, all to no avail).

I am currently in Kenya and have no recourse to telephonic assistance and can find no place to log an e-mail based official error report.

If anyone finds a conclusive solution to this problem, please take the time and trouble to post it here. Until then I am stuck working in Snow Leopard, keen to try Lion (which I have enthusiastically purchased) but unable to use the OS because of a very definite and serious bug in the way it handles DNS.

If anyone out there is kind enough to find a way to forward this to a more 'official' Apple channel it would be greatly appreciated.

I have since been able to delete System Configurations from the desktop.  Thank you.

NOOMSIE: I would try aaron 260s solution with the System Configurations file.  That basically worked for me, and this morning everything works perfectly after following Jamie-Evolution-Design's command prompts above.  Hope it works.  I was like you last night, nothing worked with network configurations. 

Did you unplug and plug again the ethernet cable to your computer..?????????????????!!!!!

Latest I've been told to do:

Go to

-Macintosh HD

-Library

-Preferences

-System Configuration

Trash all files in System Configuration, and restart.

At the risk of tempting fate, my Internet has stayed connected since.

Yep, tempted fate... Boo

I am having exactly the same issue here, connected on everything EXCEPT the iMAC that I upgraded yesterday.  HELP!!!!!!!!!!!!!!!!!!!!!

Well I managed to sort it out at last and get connected to the internet via the wireless interface.  The little culprit was little snitch 1.x was still "hanging around". 

When I was shutting down I was seeing (albeit briefly) a message about application KUC prevting shutdown.  I googled "osx application KUC"   I stumbled on this site http://www.hackerskitchen.com/mac-old/startup-items-detail.html it tells you how to disable the KUC extension.

Then I went onto the little snitch site http://www.obdev.at/products/littlesnitch/faq.html downloded the installer (need this to uninstall it).  Uninstalled the little monster and rebooted and voila!!!!!!!

My wi-fi connection was a little balky this morning after working fine all day yesterday following the Lion install. My MBA did not automatically join my network. I turned off wi-fi (formerly AirPort) and turned it back on after half a minute and now we're back in business.

Would the advice of the assembled be to wait a few days to upgrade? I was about to do this this weekend and am now thinking otherwise.