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Solved: Switches and DHCP

Discussion in 'Networking' started by Doghnut, Jan 18, 2011.

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  1. Doghnut

    Doghnut Thread Starter

    Joined:
    Jan 18, 2011
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    Apologies if this a repeat -- I searched the forum and found no duplicates.

    I run a smallish LAN at work (30-70 computers depending on the day). I am having a problem with connecting to my DHCP server through an unmanaged switch.

    I have only one ethernet port in a particular room and need to connect 3-4 computers through that port. It is my understanding that an unmanaged switch should do the trick (correct me if I'm wrong).

    The problem I have is that I cannot get more than 2 computers to get an IP from DHCP. It's a different two computers everytime -- it just seems that it's a race to the DHCP server and once two computers get there, the others are locked out.

    Various things I have tried:
    -Static IPs have no bearing.
    -Forcing a NIC to use reduced speeds makes no difference.
    -The switch is Auto-MDIX
    -The problem persists whether using regular switch ports or the uplink port.
    -I have also tried a second switch I own with the same problem.
    -Windows firewall is disabled and turning off anti-virus makes no difference.
    -My scope has not run out of IPs.

    Is there something I am missing here? I feel like the problem is simple or fundamental and I'm just not seeing it.

    Thanks in advance for any help you can give.
     
  2. PedroHin

    PedroHin

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    Aug 13, 2010
    Messages:
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    That is very strange. Right now, I am as puzzled as you are.

    With this setup, how many switches are there between the affected PCs and the router/gateway?

    From the room with the 4 PCs, how far is the next upstream device (switch/hub/router)?

    I guess you already know that as a last ditch, you can go with the DHCP reservations, and then statically configure each of the PCs for the DHCP server's reservation? With this setup, I would be interested in knowing if the 4 PCs can then all simutaneously ping the gateway IP (ping -t [gatweway'sIP]).
     
  3. Doghnut

    Doghnut Thread Starter

    Joined:
    Jan 18, 2011
    Messages:
    2
    Sorry for the long time in response -- I appreciate the help Pedro.

    Of course, I had this problem for weeks and as luck would have it, I figured it out as soon as I posted here. It turns out that each of our ports runs through a set of Cisco switches which are much more intelligent than I previously thought. I had to configure each port to accept the correct connection.

    I will mark this thread as solved in case anyone else ever experiences a similar problem.
     
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