Cox Not Giving DHCP Address to Router

Discussion in 'Networking Issues' started by roadhunter, Sep 26, 2005.

  1. roadhunter

    roadhunter Guest

    I have Cox for an ISP, and I have gone through two or three routers over the years. I am currently on a Netgear that works fine. However, in the last 2 months I have tried to install a Linksys WRT54GP2, as well as two other routers (another Netgear and a Sonicwall). None of these 3 routers will ever get a DHCP address from Cox.
    When I plug the cable modem directly into my computer's NIC, I get an address immediately. I then route the cable through my Netgear, and reset the modem, and get an address immediately.
    No matter what I do, though, the Linsksys won't get an address. I have verified that it works on another internet connection. Same goes for the Sonicwall and newer Netgear.
    Cox says there is no problem on their end, and Linksys and Netgear and Sonicwall support all say the same, as their routers work fine on other connections.
    I have tried the basics, such as cloning the MAC address of my PC, and even of the working Netgear router onto the Linksys with no luck. Host names aren't required by Cox, but I've tried that as well.
    In my 10 years as a network admin, I have never seen anything like this. Anyone have ideas?
    One more note. The Sonicwall worked fine up until 3 months ago. It still works fine on other networks....just not on my Cox connection.
  2. dethomas143

    dethomas143 Network Guru Member

    This may help isolate the problem:

    Put a hub between the router and the cable modem. Put a workstation on the hub with a packet sniffer loaded (I like to use Packetyzer - quick and free) You don't need a IP address on the NIC but you do have to have tcp/ip loaded. Set it to a static address so it doesn't try to get an address from the cable.

    Then start a packet capture and power up the router. This way you can see the dhcp request go out and responses, if any, come back. You can save the packet capture and repeat it with a device that you know works. You can then compare what's going out and what's coming back.

    This should give you some clue as to what is going on.

    David E. Thomas
  3. CrashX

    CrashX Network Guru Member

    Old thread, I know, but I found it while searching for something else and thought I'd add a response.

    More than likely, the MAC addres from your PC has been cached by your cable modem, and subsequently, Cox. Since Cox only allows a single computer to get an IP address (unless you pay for more), they see the MAC address of the router as a second computer and deny the DHCP request.

    Look on your router for a MAC address clone feature, and give it the same MAC address that your PC has. You should be fine after that.

    As an alternative, you might be able to shutdown the cable modem, reconnect the Linksys to it, and power everything up again. A power reset of the modem usually clears the cached MAC addresses.

    (This has been my experience with several customers of Cox when they install a router for the first time. In all cases, the modem used was a Motorola SurfBoard.)
  4. whatsthedeal

    whatsthedeal Network Guru Member

    I agree with CrashX here.

    I just wanted to share the easiest way to get your mac address on a windows pc (in case you don't know):

    start - run - cmd [enter] - ipconfig /all [enter]
    where [enter] means hit the enter key on the keyboard
    (i'm used to explaining this to people 60+ years old so sorry if you already know this)

    the mac address you need will be the one which has an ip address of 192.168.*.* when connected to the router. if you only have 1 network adapter, just use the MAC address listed.

    EDIT: i just realized that you said you're using a netgear router so you can try to clone this address. it's probably listed on the bottom of the router.

    either way, try unplugging the modem and router and plugging them all back together like CrashX said
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