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Networks: How routers assign DCHP LAN IPs? - Mac Networking

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    Default Networks: How routers assign DCHP LAN IPs?

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    morenuf Guest
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    Default Re: Networks: How routers assign DCHP LAN IPs?

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    Christoph Guest
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  3. #3

    Default Re: Networks: How routers assign DCHP LAN IPs?

    In article
    morenuf <com.invalid> wrote:

    Dependent on the DHCP server and DHCP client configurations.

    Inso far as the client is concerned from

    "Different versions of Open Transport behave differently when
    discovering, renewing, and releasing a DHCP lease. This article
    describes the behavior of the DHCP client in different versions of Open


    Loading IP in this manner does not attempt to keep the same IP address
    when a computer is restarted. Depending on the DHCP server
    configuration, the client may receive a different IP address every time
    the IP stack loads.


    The DHCP client was modified in Mac OS 8.5 so that the client would
    attempt to regain the previously assigned IP address if the lease is
    still active when the IP stack loads. This makes it much more likely
    that a computer retains the same IP address when it is restarted.

    .... "

    My experience with the two DHCP servers that I interface with currently

    1. My ISP's DHCP server... I always get the same IP address unless I
    change the MAC address at the ISP's web page.

    2. My Airport Base Station's DHCP server. It appears to assign IP
    addresses on a first come, first served, basis from up when
    the whole network is first initialized. On subsequent requests and
    reboots, reassigns the previously held IP address.

    Configuration of LAN, 2 wired Macs running 7.6.1, 2 wireless Macs
    running 10.3.4, 1 Airport Base Station, 1 ADSL modem.



    To reply, substitute .net for .invalid in address, i.e., darrell.usenet2 (at)
    Darrell Guest

  4. #4

    Default Re: Networks: How routers assign DCHP LAN IPs?

    In article
    morenuf <com.invalid> wrote:

    Thanks to all who responded with advice, comments, information.

    I found the culprit after about a week of investigation (and not really
    knowledgeable about networking issues or OSX).

    4 years ago I setup my router. One setting was DHCP (which I did not
    use for 3+ subsequent years). It had a basic starting address like and a range, plus a dialog box to enter number of
    computers. I had put in 3 computers (I had only one at the time) which I
    thought was enough.

    2004. Now I have 4 computers and had just added the iMac. That made 4
    computers trying to get 3 addresses. No wonder I had seeming conflicts
    and one or more computers seemingly confused. The computers could only
    get 3 addresses for 4 machines! Booting, rebooting, sleeping etc the 4
    comuputers in various combinations only made a mess trying to figure
    this out.

    Corrected the situation by changing it to 4 computers. Now all 4 get
    DCHP assigned unique IPs.

    Cute little wrinkle adding to the confusion. My router
    MacSense MIH 130A XRouter Pro (
    configuration is done through a web browser. Safari would show the info,
    change it, all would look okay, but change would not hold. Safari just
    plain would not work. Used IE and the changes held. NUTS.

    Don't know why Safari would not work. It would show the current info
    fine, but not permanently change or update the configuration in the
    router, even though on screen it indicated it had done this.


    Still don't know (or predict) who gets what IP numbers, which seems to
    be more that bit random, depending on which computers are on, which are
    asleep, the order they are turned on, timing of when the router is
    reset, etc.

    The only help I have here, is IPNetMonitor which has tools to query the
    local network and get an address scan. It lists the active computers ,
    their IP number, and a MAC (hardware) address. As no names appear in
    IPNetMonitor, Apple's Network tools, the Go menu "connect to server"
    etc, the only I can decipher who's got which IP is to learn the MAC
    address and use the IPNetMonitor tools to figure it out. I could go to
    each computer physically, Network, and get that info too. But a real
    pain in the x.

    All this would be less of an annoyance if a NAME of some sort was
    attached to each machine so I could identify the computer in the
    bedroom, basement, or where ever. But Apple's tools don't have any names

    For example, to connect to the DELL for file sharing, I have to use a
    full path name like SMB:// IP number. If I can't know the IP
    number in advance I have to do detective work at that instant in time to
    determine it. NOT a USER friendly design.

    Oh well, it was educational.

    Thanks for the help. It is appreciated.

    morenuf Guest

  5. #5

    Default Re: Networks: How routers assign DCHP LAN IPs?

    In article
    morenuf <com.invalid> wrote:

    Why don't you change it to something like 100, so you won't have to
    worry about this the next time you add a computer?

    Probably bad HTML in the form, so the button to apply the changes is not
    working right. Many web page designers only test with IE and maybe
    Netscape; they assume that if it works for them, it must be correct.

    Most DHCP servers will try to remember past assignments and reuse them
    if possible. Since you had fewer addresses available than clients, it
    wasn't always able to do that, so the addresses got shuffled around.
    Try bumping it up to 100 like I suggested above, and it may be more
    consistent. But the initial assignments are likely to be first-come,

    Some routers have a page in their configuration interface that shows all
    the address assignments.

    The should may have a configuration page that allows you to assign
    static IP's to particular MAC addresses. It's a good idea to do this
    for a server.

    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
    Barry Guest

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