Troubleshooting Network Connectivity (3)

June 7th, 2008

The TCP/IP network that most people use today is not really a plug-n-play thing.  It needs proper configuration.  Typically I follow these steps to figure out if the network configuration is correct or not.

  1. Do I have an IP address?
  2. Do I have a working name service?
  3. Can I reach the machine that I want to connect to?

The most basic and important part of network configuration is to get a valid IP address.  One can simply use the ipconfig tool to tell if there is a valid IP address (i.e. something other than or 169.254.*.*).  We can further drill down the possible reasons of not having a valid IP address

  1. No actual network link is established (typically happens in wireless network)
  2. DHCP down
  3. Misconfiguration

Wireless devices today typically negotiates well with the wireless router.  However, if you want the wireless link to be secure, you’ll need to enable WPA or WPA2, which requires setting up passwords to connect to the router.  I find that the problems often come from the tools that shipped with wireless routers/adapters to “help” user setup these configurations.  From my personal experience/bias, these tools creates more problems than the problems that they intend to solve.  Here are some rules of thumb that I’d suggest

  • Do not install additional programs unless absolutely necessary
  • If there is a Windows build-in device driver for the wireless adapter, and there is no strong evidence saying that vendor-provided drivers perform better, use the Windows one.  It’s not a 3D-graphics card and there’s typically little performance difference between Microsoft and vendor drivers.  More than often, you don’t really need the add-on features provided by vendor drivers.
  • If you can install device driver through Device Manager in Windows, do it that way.  I’ve seen too many ill-written setup programs of wireless adapters that do lousy jobs and screw the registry.
  • IMO the best way to do WPA configurations is getting them done through the web interface of router and through the Windows Control Panel.  Remember to write down the passwords and settings.

The criteria that we have an actual network link to the router is that you can ping the router (say, ping and found it’s responsive).  Remember to turn off your firewall program when you ping because some firewall can block the ping (ICMP) traffic.

DHCP is a nice tool to have, and most routers today have built-in DHCP server.  However, if you don’t have a IP address, and the network link is okay (i.e. you can ping the router), I’d then suspect DHCP server is down.  A router can still be operational even though its DHCP server is not working, so power cycling the router is typically a worth try.  (Just think that the router is a small computer running programs, and DHCP server is one of these programs so it could be dead while other programs running normally.)  Again, you’ll need to disable the firewall, do “ipconfig /renew”, and see if you can acquire an IP address from the DHCP server.

One problem that I often see is that people have statically configured their network in the beginning (with some guru’s help), and then purchased new equipments and run the auto-configuration tool.  There’s little chance that the auto-configuration tool will respect existing network configuraions and setup accordingly.  As a result, you might have some computers configured as 192.168.1.* while others as 192.168.2.*, which by no means will work.

The other typical misconfiguration is that people have two routers and try to setup them in a single network segment (i.e. an old wired router as and a new wireless router as  You can not have two routers in a single segment.  If the numbers of IP address really matter, we can play netmask tricks and setup static routes so every device has a 192.168.1.* address, that’s one way to do it.  The other way is to downgrade the wireless router to AP or the wired router to hub, so there’s only one router in charge.


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