Strange Network Problem

By Runtest
May 15, 2009
  1. This is a whopper and I need to figure it out so it does not happen again.

    The Setup:

    We have around 20-30 computers running Windows XP Professional. They are connected to a patch pannel and re-directed to 4 16-port linksys switches, all brand new. They are each linked to each-other by one wire, I am very carefull not to create unneeded loops.

    We have a server that acts as a domain controller, dns and dhcp controller. It has an address of 1.3 for the server and 1.4 for out going. These are also connected to the switches.

    We have a router with DHCP turned off acting as a gateway leading to a simple Motorola modem. The router only has one connection to one port of the switch.

    The Problem:

    There is one computer a customer brought in and I will be frank, I am making this sound simple but it had us down for 2 days. We finally unplugged everything except one laptop and the Internet started working again. When we plugged in this cable it gave a connection back to this evil laptop we were fixing. The Internet would quit working instantly.

    What could be on a computer, that when plugged into a network, would allow full Intranet access but no Internet access?
  2. gguerra

    gguerra TS Guru Posts: 319

    I assume you tried different patch cables and ruled that out. From the sounds of it your "evil" laptop has a defective ethernet port on. It could be shorted out internally or on the port itself. Unfortunately unless you have good soldering skills and can take the laptop apart without any problems it will be difficult to fix. We are not sure that is the problem but that is what makes sense. You can get a cheap wireless router, plug it into your switch, configure it as an access point and connect your laptop via Wifi. Oh and forgot to ask, when you say the internet stopped working, did your LAN connectivity stop working as well? If it did not than that is truly a mystery, if it did make your LAN stop working then the bad port idea may be the case. In any case you will have to do some further troubleshooting.
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