Problem configuring with DHCP

[dogbone]

I wasn't sure how best to title this thread.

Anyhow I've got two emacs connected to the net with a router. There was a bit of lightning problems and the power went out. One mac was unplugged and one wasn't. The one that was plugged in had all the internet setting removed.

After reconnecting with auto configure I eventually discovered that one of the ports on the router is not working. Ok so I used a different port. Then I discovered that the other emac is now not connecting to the net. Anyway I've bypassed the router and I'm just connecting each emac one at a time to see what the problem is. This is what is happening.

I plug computer A directly into the Modem, go to network setting and add a new location then select "TCP/IP" then configure "Using DHCP" then "Apply" and I can see that an IP address comes up, then a Subnet Mask address then a Router address and I can connect to the net.

However when I try the same sequence on the other computer with it directly plugged into the modem, and click "Apply Now" I get an IP address, a Subnet Mask address, but I do not get a Router address come up and I cannot connect to the net with it.

I don't understand this at all. I'm bypassing the router that I use to usually have both computers connect to the net. So when I try each one individually one of them shows a router address and one doesn't?????

I hope this is clear.

 

[dogbone]

I've narrowed the problem down to this.

When I use the auto configure for one mac it sets up an IP address of 10.0.0.1 and a router address. This works,

when I use the auto configure on the other mac it sets up an IP address that looks like a normal IP address with lots of numbers, and no router address. This does not work.

I guess the problem must be in the mac somewhere but I can't understand why it is happening.

 

[Makosuke]

Sounds like what you're describing is pretty simple: One computer is pulling DHCP info from the modem/router, one isn't.

There are a few things that might cause this:

The worst option would, given that this happened during an electrical storm, be that the one that isn't working had its ethernet port fried. If there was a dead port on the router you were using during the lightning issue, this seems VERY likely. A couple of things you might try to narrow it down: Is the "network" light on the modem lighting up? If not, it's not even negotiating a connection--bad sign. Also, try opening up Network Utility when it's connected to the modem--under the hardware info section, the ethernet port (probably en0) should show link status as active even if it isn't getting any DCHP info--if it says inactive, also a bad sign. You could also try starting it up from the hardware test disc and seeing if that gives any errors--if so, uh-oh.

If the hardware IS negotiating a connection but it's just that the DHCP isn't pulling the correct network info, then it might be an issue with the modem--perhaps it is set to only give out a DHCP address to one device and it's "bonded" to the working Mac's MAC address... but that doesn't strike me as likely, and power cycling the modem should fix it. That also wouldn't explain why it wasn't working with the router.

If it's software, I'm not sure why it might be happening. A restart fixes most things of that sort, but I'm assuming you've done that. Reinstalling the OS from scratch might clear it up, or booting from an external disk to test if you don't want to screw up your current OS install.

Good luck, and I hope it's not hardware--if it is, you're kinda out of luck with an eMac since the port is on the motherboard and there's no way to add a card or such. If that turns out to be the case, you COULD use a firewire cable to link it to the other eMac and use Internet Sharing to feed it a network connection. I've never actually tried that, but in theory it should work.

EDIT: Oh, one thing I forgot; just to check, the one that's having problems DOES have the ethernet interface enabled, right? And under the Ethernet tab of the Network pref pane, it is set to configure Automatically, right? That shouldn't be wrong, but if some setting got screwed up, maybe that did too.

 

[dogbone]

OK it's fixed, turns out a restart fixed the problem. But I didn't think to restart because the mac that was having the problems is not the one that was plugged into the router port that got fried. That one was restarted and I had to reset the DHCP as well. Both computers were connecting fine, then suddenly the other computer that was unplugged during the storm stopped connecting. It's a bit of a mystery really. But at least I got away with frying the router port and not damaging the computer, so that was pretty lucky.