Make a New Location, Using network locations in Mac OS X ...
10.7 & 10.8…
System Preferences>Network, top of window>Locations>Edit Locations, little plus icon, give it a name.
System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.
The interface that connects to the Internet should be dragged to the top of the list.
Is that Interface dragged to the top of Network>Show:>Network Port Configurations.
If using Wifi/Airport...
Instead of joining your Network from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.
For 10.5/10.6/10.7/10.8, System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...
Here's what I did:
Because I am using wireless with an Airport router, I clicked on Advanced, and added the two IP addresses in the DNS tab, and exited with OK.
Now I'll wait and see if my ability to connect with my various email servers is improved.
I'll add another reply in a few days if all is well, or sooner if it is not.
What that all does is make new files for network connections that may be messed up or conflicting.
DNS Servers are a bit like Phone books where you look up a name and it gives you the phone number, in our case, you put in apple.com and it comes back with 18.104.22.168 behind the scenes.
These Servers have been patched to guard against DNS poisoning, and are faster/more reliable than most ISP's DNS Servers.
Yeah, but it's happened again. Here are a few more facts. The cable modem feeds an airport router, and we have another computer, a PBPro, which does not suffer the same symptom. The other computer is not running Safari nor is it running Apple Mail. It operates just fine with Firefox and MS Entourage, while mine loses its ability to connect with mail servers or new web sites.
So when the computer in question, my iMac, stopped getting email, and also would not open a new page in Safari, all I did was restart it. Everything was OK after that.
So does this suggest any other strategy for keeping this ting from happening every day or two?
I don't know how to check the IP's of everything connected. My best guess is that I need to find the IP address of the 4 units that are on the wireless network - the other computer, my iPod touch, and my iPad. How to do that??
And are you thinking that as one gets connected, it is using or usurping the IP address of my iMac?
That's what I'm thinking at this time, unless matbe the Router is set to only allow a small range of IPs to be habded out.
Can you test one at a time not connected to see if the iMac stays connected?
I think this is what you are suggesting: I'll take my iPod touch off of wireless, using its settings app and then see if my iMac remains connected properly for a fw days in a row. If it does, then i'll put my iPod back on wireless and see if the iMac has a failure in the next day or so.
If this happens, then it shows that somehow my iPod is bumping off the iMac from its connection.
But does this fit with the fact that restarting my iMac restores its connection every time?
It happened again. While the iPod Touch was offline, with the PBPro connected and the iPad connected through wireless, all my email servers were unavailable, and Safari was unable to open a new address.
Upon doing a Restart, all was OK again.
A little history: This trouble started only a couple of months ago. The three devices, iMac, PBPro, iPad, were sharing a cable modem connection for over a year before with no problems. I got the iPod Touch sometime in the fall, and it was almost always on the wireless network for a couple of months before this symptom appeared.
I think it is evident that this problem resides in my iMac, because the other devices can access the internet even while the iMac comes to an isolated state.
Should I try to move over to a new user on the iMac, just to run Mail and Safari and nothing else? Would that help isolate the problem?