Partager via

Troubleshooting a Local Network

  • Article

I just spent a few hours on the phone with my friend Mike Loftin diagnosing problems with his local-area network (LAN).  Mike had recently bought a new machine with Vista installed and wanted to get it working wirelessly on his local network at home.  His problem was that it connected to the local network but not the Internet.  After playing around with IPCONFIG and the "Network and Sharing Center" on Vista, we figured out that he wasn't getting the correct DNS information.  He had an old DNS setting for when he used to use Comcast as his ISP - now he's using QWest.  We eventually figured out that Mike had a somewhat screwy configuration of his LAN, for historical reasons.  This probably applies to a lot of people.

What happens is you start with a single computer and a DSL or cable modem, which you connect directly to that machine.  All is good.  Then you get a second machine.  So what do you do?  Typically, you buy a router which enables you to create a local-area network.  Now the "right" thing (or perhaps best thing) to do is isolate the DSL modem from the original computer and plug it directly into the router, then have all the computers (both of them in this case) plug into the router.  However, DSL modems these days are smarter than they probably should be - they sometimes have wireless capability built-in and they have built-in DHCP servers.  When you buy a router with these capabilities as well, you potentially create a problem - you now have two DHCP servers on your network, one from the router and one from the DSL modem.  If you leave the DSLmodem plugged into the original computer and just use internet connection sharing to add the router (which is what Mike did) you have even bigger problems - because the original computer is also acting as a DHCP server (through internet connection sharing). 

So ideally you take a bit of time and do the following:

1. Turn off the DHCP capabilities on the DSL or cable modem - have it just be a simple modem.

2. Plug it into the router.

3. Redo the connections from all LAN computers to the router (whether wired or wireless).  Make sure the router has the DHCP enabled and has the right DNS settings or is set to automatically get the DNS info from the ISP.  Typically, you configure this by opening a browser on a machine connected to the router and type in an address like https://192.168.0.1 (the manual will give you the exact address) which lets you talk to the software on the router to control its configuration.

4. Have all the computers join a common workgroup - you set this in Computer Properties (Start / Computer / right-click and select Properties on Vista) - look down for Computer Name, Workgroup and Domain settings and click "Change Settings".  Two things are important: (a) each computer has a unique name and (b) they all have the same workgroup name (doesn't matter what it is, as long as it is the same). 

5. Reboot everything.

More info at https://www.microsoft.com/windows/products/winfamily/mobility/articles/homenetworking.mspx and https://windowshelp.microsoft.com/Windows/en-US/Help/b27b71d8-4098-47c8-ad95-05f51e49cd121033.mspx.

Comments

  • Anonymous
    October 15, 2008
    Interesting post, haven't used it yet but after reading this will give it a try. Thanks.

  • Anonymous
    March 17, 2009
    unique hostname and set the 'lan connection' property to 'obtain the ip address automatically' will work. Thanks mate.