View Full Version : Adding an iMac kills my WAN access.

14th March 2010, 03:32 PM
I've got a really odd situation that I can't seem to resolve.

Essentially, my home network has no problems whatsoever while it's limited to the usual configuration:

- 3 desktop computers connected via ethernet to my TP-LINK Modem/Router.
- 1 laptop connecting wirelessly to same.

None of these are Macs.

The problem arises when my friend brings over his iMac.

When he tries to connect to the network wirelessly, the network dies. None of the other PCs can access the Wide Area Network. The LAN remains intact but the WAN becomes inaccessible. The same happens when we connect the iMac to the TP-LINK Modem/Router via an ethernet cable. Somehow, it manages to kill off our WAN access.

Only after the iMac is disconnected, Airport shut off, and the router reset does everything begin working again.

However, the moment the iMac is reconnected to the router via ethernet or wirelessly, WAN access is rendered impossible.

I've tried dozens of troubleshooting options in hopes of solving the problem, so I won't list them all right away. I was hoping someone might be able to make a few suggestions that I've not yet considered.

I have no experience with Macs, so I'll concede I'm at a disadvantage. However, my brother-in-law is a hardcore Mac enthusiast -- he even makes a living teaching people how to use Macs -- and he, too, was baffled by the problem.

We've tried a different Modem/Router and the same problem arose. We've discussed the problem with our ISP (Internode) and they couldn't shed any light on it either. We've examined the Mac's update logs, updated the router's firmware, experimented with different cabling, etc. Nothing helps.

What's really strange is that the iMac had no trouble joining the network for the first 4-5 weeks of my friend bringing it over. These problems arose out of the blue ...

Any ideas / suggestions would be greatly appreciated.

14th March 2010, 03:50 PM
So does the WAN light on the modem/router stay on or just switch off when you try to connect with the mac? Maybe try booting the Mac from a clean system on an external drive if you have access to one.

14th March 2010, 04:18 PM
Maybe your friend's iMac is attempting to make a PPPoE connection - ie. trying to authenticate to his/her ISP - and hence killing your own connection.

14th March 2010, 08:00 PM
Or the iMac may have network sharing switched on (which turns on a DHCP server on the Mac). 2 DHCP servers on a network means nothing works. There's a DHCP server in your router.

I would recommend going into Network in System Preferences, going to Location, and Edit Location and create a new blank location named after your house. Then try to connect.

15th March 2010, 01:19 PM
Thank-you so much for the replies, everyone.

I feel genuinely awkward about posting this follow-up but for some reason, the problems didn't arise today. At all! We hadn't changed any configurations; hadn't tried anything new; hadn't altered any settings ... everything just worked. This, after a month of nothing working, no matter what we tried!

I'm as baffled by this outcome as I was the problem itself. I'd held off on creating a thread for well over a month because I didn't want to waste anyone's time with a problem that I assumed I'd be able to fix on my own.

I don't know whether to be happy or irritated. On the one hand, it's all working flawlessly (via ethernet and wirelessly) ... on the other hand, I never found out the cause of the problem.

I'll definitely keep this thread bookmarked in case it happens again.

In the meantime, I must thank you again for the suggestions. They may prove helpful in the future, so I hope you won't consider your efforts a waste of time.

15th March 2010, 05:36 PM
LOL - it's the law of IT Helpdesks: As soon as you get someone to look at your machine, the problem goes away.

I'm glad your problem has gone away, and hope it does not reappear again soon.