No announcement yet.

Weird DHCP scope filling with bad addresses

  • Filter
  • Time
  • Show
Clear All
new posts

  • Weird DHCP scope filling with bad addresses

    Network is a Data VLAN/Voice VLAN with IP phones.

    At first I had it in my head that this issue was just a problem with MY windows 2003 DHCP server, that is until we had the exact same issue on another totally isolated and different network set up by someone else. The scopes are filling up with BAD_ADDRESS and the weird thing is that the MAC addresses are not valid MAC addresses. They look like 1/2 of a HEX MAC. This number converted to decimal and then reversed is a valid IP address on my voice VLAN.
    I think this issue maybe has something to do with the way the IP phone(s) are requesting DHCP.
    The phones issue a request and the Data VLANs DHCP server responds with an IP address and a special option that tells the phone to switch VLANs. The phone reboots and requests a DHCP lease from the voice VLANs DHCP server. It all works but the Data DHCP scope fills with BAD_ADDRESS until its exhausted. It's like the Data IP's are not releasing after they are abandon by the phone. We have tried conflict detection.

    I did find one mistake where the DHCP server's switchport was set to TAGGING in the voice VLAN but removing the TAGGING didn't help.

    We have put DHCP on the router at both locations and that seems to work ok.

    Has anyone ever heard of this?


  • #2
    Re: Weird DHCP scope filling with bad addresses


    What is your OS, how many DHCP server, (seems like you have multihomed clients and single dhcp server). How many nic on DHCP server, are both servering the clients, are they connected to same segament or different.

    A topology diagram for your dhcp network would help us to understand.
    Thanks & Regards

    MCTS 2008, MCTIP, MCSE 2003, MCSA+Messaging E2K3, MCP, E2K7
    Sr. Wintel Eng. (Investment Bank)
    Independent IT Consultant and Architect

    Show your appreciation for my help by giving reputation points