Computer on the netwotk won't connect

Posted on 2004-11-16
Last Modified: 2008-01-09
Hi guys,

I have a network with 14 computers and 3 servers.
Servers are running server2k and all computers are runing winxp.
I have one deomain controller with active directory and a DHCP service.
I have 3 room with 4 computers all connected though a hub and all hub are connected to the network to a swicth (3com 3C16471) except 2 computers that are connected directly to the switch.
In order to improve the connectivity in the whole network i decided to redo the network.
So i placed network cable for every computer (each one is directly connected to the switch).
All cables are tested and work perfectly.
In the previous configuration, computers that were directly connected to the switch work in the new configuration but alle the other computer won't work and i'm facing the following problem:
- Some can't get an IP address from the DHCP and are assigned a default address that starts with 169 that limits the connectivity, => no internet no nothing.
- Other computer just display the "a network cable is unplugged" notification (all cables work perfectly are tested so cables are not the problem)
I spent a lot of time redoing the network and i don't want to go back to the old configuration.

Do you have an idea of what is the problem and how do i fix it?

Please help

Question by:Ygal_Benabou
    LVL 4

    Expert Comment

    Try hardcoding the speed and duplex settings on both the PC and the 3COM switch.

    LVL 7

    Accepted Solution

    Was the hub a 10 MB hub?  If so, some of the cables or data line runs that you are using may not be rated for 100 MB and won't work with your switch.  How did you test your lines?  The switch is capable of running at both speeds, but your cables may not be.  That said, the autosense on some switches is less than reliable when old cabling is involved.

    Usually the error you are getting means a physical connection problem.  I'd be tempted to take one of the machines that isn't working into the room with the switch and plug it in directly with a cable that has worked with that switch before.  If it works, you probably have some cabling issues.

    Good luck.

    Expert Comment


    It sounds like you are just going to have to troubleshoot this back to the point of failure. Currently its not known if it is client config / cable/ switch / or a DHCP server issue.

    1. Perform IPCONFIG /ALL on a workstation that is working - that gives you an idea on the configuration requried for all machines to work.

    2. On a workstation that isnt working and does have a link light, try the following commands:


    Then... IPCONFIG /ALL    > Compare this to a computer that is working?  

    3. If you do not get an IP address, try setting a static IP address on the workstation with the same network as the DHCP server and then see if you can ping the DHCP server. If you can, this is starting to suggest that the DHCP server configuration may be the issue? If not, you have to check cable/switch configuration. Try swapping the cable and switch port with a computer that works and use it in the one that gets the 169 address?

    The 3COM switch that you have is a low/no conifig switch, any port should work.

    4. If you where using Hubs you may have cross over cables in the mix there, double check that none of the cables are cross overs.

    Hope this helps!
    LVL 9

    Expert Comment

    How did you connect your hub to a swtich? Did you use  straight cable or cross cable?
    LVL 3

    Expert Comment


    1. Reset the switch

    2. what happens with the port-leds on the switch
        if they are on you're physical link shoot be OK (it still an indication, not a fool test)

    3. test in a 10MB env.
       a. go to the properties of local area connection
       b. choose configure at the network card
       C.. click on the tab advanced
       D. in the list select something like media type
       E. select in the combo box 10 MB
    LVL 3

    Expert Comment

    soory guys my english isnt so good in the morning
    LVL 9

    Expert Comment


    What is the maximum distance on the cables form end - switch ?.

    What is the LED status on the switch for the PC's that is not working ?...
    What is the LED Status for the PC's NIC ?.

    Unfortunately it's a unmanged switch so we can only go from the LED's...


    Author Comment

    Both leds are flashing in a one second interval while the other taht are connected the leds keep lit and are not flashing.

    Expert Comment

    Sounds like you have a physical problem. This switch auto negotiates MDI/MDIX so cross over cables would not be a problem.

    How did you test the cables. The blinking LED's are a sign that it is getting some type connectivity but possible high errors. Are the connection problems with the computers that are the farthest from the switch?

    Here are 3 things I suggest you do.....
    1. Take a computer/laptop to the location where you have the switch and plug it in there. Do you have connectivity, get an ip address and have access to the internet? If you do then the connectivity to the internet and DHCP server are good from the switch.
    2. Take that same computer that just worked to one of the connections that is connected but not getting an address. Try hardcoding an address and see if you get connectivity. Can you ping the DHCP server from there?
    3. Take the computer to a connection that does not get a link light or no connection to make sure that it is not related to that computer. Check that cable and verify that the cable is made according to this link.... . To meet specifications the cable must be shorter than 100 meters. If you cables are 80 meters or more then you will want to make sure that the cables are not ran near any type of electrical source. The longer the cable the more interference will make problems.

    Good luck

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