DHCP Followup RE: Requesting new IP address RH 9

From: Ben Yau (byau_at_cardcommerce.com)
Date: 01/12/04

  • Next message: Ben Yau: "RE: RH9 Processes Failing" 
    To: <redhat-list@redhat.com>
Date: Mon, 12 Jan 2004 14:29:08 -0800

    > Another idea, something easier to try out (it may cause some havoc):
    >
    > you could see if putting a duplicate IP out there would work.
    > Get a second
    > machine next to your first one and put a fixed IP on it with same
    > IP as your
    > DHCP client. Stop/start your DHCP client network interface (or reboot),
    > making it ask for a new lease. Perhaps the DHCP server will see the IP
    > addres on the network (in this case you're second machine) and decide to
    > send a different one. Or perhaps your client will see the
    > duplicate IP and
    > refuse and ask for a new one.
    >
    > Just throwing out more ideas. If you try any of them let me know :) I'm
    > curious .
    >

    Hello all.

    Just a followup. I read the rfc 2131 over the weekend. Here is a summary
    of the section about reusing allocated IP addresses.

    1. DHCP server does NOT check the validity of the address on its first offer

    2. (paraphrase)
    "If the client detects that the IP address [which the server allocates to
    the client] is already in use, the client MUST send a DHCPDECLINE message to
    the server and restart the configuration process by requesting a new network
    address.

    3. (quote)
    "If the selected server is unable to satisfy the DHCPREQUEST message(e.g.,
    the requested network address has been allocated), the server SHOULD respond
    with a DHCPNAK message."

    [ben - basically server acknowledging client's notion that it cannot accept
    the first address the server sent]

    4. (quote)
    "If the client receives a DHCPNAK message, it cannot reuse its remembered
    network address. It must instead request a new address by restarting the
    configuration process, this time using the (non-abbreviated) procedure"

    A bit convoluted, butwhat it means is theoretically the duplicate IP trick
    should work if your DHCP client and DHCP server are written to protocol. I
    did'nt have the time or energy to set up a DHCP server at home and try it
    out so I hope someone has the time to try this out and let us know if it
    works :)

    Cheers-
    Ben Y 

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