Originally posted by l008com:
<STRONG>I just got a BRAND NEW problem. When I try to run software update out of the System Preferences App, I get an error saying, "Software Update is not able to connect to the Internet. Please check you configuration and try again." But I am connected to the internet, all my other apps are running fine, my router is running fine and my web sites I host off my machine are all up. Everything seems to be working great, except Software Update. I even restarted my Mac and my router, just for the hell of it. I assume that the Software Update server is just down or something. Anyone else having this problem (everyone I hope, or else im screwed.)</STRONG>
While it may be a problem with Apple's servers, it might also be a problem with your software update app. I had a similar situation on one of my machines a while ago.
Here's the way to debug it.
For sanity's sake, quit all other applications.
Open Preferences -> Software Update, and a separate Terminal window.
In the Terminal, enter
sudo tcpdump -i <interface> -s 128 where <interface> is the name of the connection you use to connect to the net, usually en0 or en1.
Once TCPDump is running, click the 'Update Now' button in Software Update.
Now, the TCPDump output can be a little hard to understand, but the first thing you should see is something like:
<font face = "courier">16:33:46.235339 172.16.1.100.62814 > ns1.domain.net.53: 35650+ ANY?
www.apple.com. (31)
16:33:46.258677 ns1.domain.net.53 > 172.16.1.100.62814: 35650 1/4/4 CNAME
www.apple.com.akadns.net. (232)
16:33:46.263544 172.16.1.100.62814 > ns1.domain.net.53: 9823+ ANY?
www.apple.com.akadns.net. (42)
16:33:46.287343 ns1.domain.net.53 > 172.16.1.100.62814: 9823* 1/0/0 A
www.apple.com (58)
</font>
In layman's terms, the tcpdump is showing your system performing a DNS lookup on
www.apple.com. The most important part is the "1/4/4 CNAME <A HREF="http://www.apple.com.akadns.net."" TARGET=_blank>www.apple.com.akadns.net."</A> which is the DNS Server's reply.
You see, Software Update performs a name lookup on
www.apple.com to determine if you have a valid network connection or not. If the DNS Server responds "1/4/4" then it found an answer. If it replies "0/0/0" then no answer was found and Software Update will assume you have no valid network connection.
If that test passes, Software Update tries to DNS lookup swscan.apple.com (which is where is downloads a list of latest updates), so you should see a similar process when Software Update does another name lookup.
If that works, you should then see Software Update try to connect to swscan.apple.com on port 80. If there's a problem on Apple's end (e.g. servers overloaded, down for maintenance, etc.) then this transaction will fail and you'll just have to try again later.
That should be enough to tell you where the problem lies.
tcpdump, while arcane in its output, can be a very powerful debugging tool.