OK, geniuses, let's see if you can figure out this little problem that just happened to me. I figured it out, and it's solved now, but it's obscure.

Here are the players in the game:

Regulus -- the Qube, through which everything flows.
Railgun -- the new combined ethernet/wifi hub
Zako -- the old SMC ethernet hub
Deneb -- the Windows Home Server
Alcyone -- the super notebook.
Saten -- the Slate
Arcturus -- the Compaq notebook I run uTorrent on

Alcyone connects by wire to Railgun.
Saten connects by wifi to Railgun.
Railgun connects by wire to Zako.
Zako also connects by wire to Arcturus and Regulus
Regulus also connects to the cable modem.

All the other machines use NAT on Regulus to access the internet.

My torrents suddenly turned off and stopped running. That's where the problem first appeared. Arcturus could access Deneb as a file server just fine, and it could load my private start page off of Regulus, but it had no other network connectivity. DNS always failed, and IE couldn't load anything off the net.

Meanwhile, Alcyone was working just fine. Saten had no problems.

Then I tried rebooting Alcyone -- and it no longer had internet connections, even though it could access Deneb just fine.

Here are some things that made no difference: power cycling Zako. Power cycling Regulus. Power cycling Arcturus.

I also tried disconnecting the ether net on Arcturus and enabling its wifi. It was exactly the same: it could access Deneb, but not the internet.

Here's what did fix it: Power cycling Deneb, and once it was back  up then power cycling Alcyone and Arcturus again. After which everything worked beautifully.

See if you can figure out why.

UPDATE: Here's a hint:

I used a utility to look to see what IP each computer was using. Arcturus was something like this: 169.254.144.173. When Alcyone no longer worked, its IP was something like 169.254.198.87.

When I saw that, I figured out the problem.

UPDATE: Here's the answer:

Deneb runs a DHCP server. It's set to serve IPs in the range of 169.254.101-199. The IPs that I found for Arcturus, and Alcyone when it stopped working, were outside the subnet range that Regulus is set for. Regulus's IP is 169.254.1.1 and its subnet mask is 255.255.255.0.

So Arcturus and Alcyone couldn't make contact with the Regulus NAT because they were out of the subnet. But they could talk to Deneb as a server because Windows networking doesn't use TCP/IP. It's an entirely separate protocol that runs over ethernet. (And it also works over wifi.)

Arcturus stopped working because the previous DHCP lease had run out. It tried to access the DHCP server on Deneb, and for some reason that didn't work. (I'm not just sure what the deal was. The DHCP page on Deneb showed that it had reissued IPs to all the machines in question, but they never heard it.)

Alcyone stopped working when I rebooted it because a reboot results in a new DHCP request, which failed.

The reason they had the IPs they did is because that's the rules. If a computer is told to use DHCP on boot-up and cannot find one, then it picks a random IP in 169.254.*.*.

So rebooting Deneb caused the DHCP server to restart. Rebooting Arcturus and Alcyone caused them to make DHCP requests for new IPs, and it worked properly, giving them IPs within the Regulus subnet.

Posted by: Steven Den Beste in Computers at 06:34 PM | Comments (7) | Add Comment
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