DHCP reservation renewal

Discussion in 'Windows Networking' started by Ckuderna, May 13, 2008.

  1. Ckuderna

    Ckuderna Guest


    I guess this is a very simple question but I couldn't really find any
    documentation on it:
    - clients that have a reservation in DHCP show up with a lease
    duration of INFINITE in the address leases list
    - usually a client tries to renew its lease after 50% of the lease
    duration has expired. What's 50% of infinite? ;-)

    Does the lease duration setting on the scope (e.g. 8 days) also apply
    to the reservations?
    If yes, does that mean that in this scenario the client should renew
    its lease every four days? The DHCP server is configured to always
    update A- and PTR-records.

    I'm wondering because some printers connected through JetDirect cards
    (with reservations) receive the correct addresses but it seems like
    the DNS entries never get updated after they are initially created and
    consequently are scavenged by the DNS server sooner or later. Turning
    the printer on and off solves the problem but is not an option for us.

    Thanks for your help
    Ckuderna, May 13, 2008
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  2. In
    Mathematically speaking, 50% of infinite is infinite. :)

    To optimize JetDirects registering in DNS, you can force DHCP to register
    for clients that cannot register (DHCP properties, DNS tab), such as a
    JetDirect, which can't update itself. But when DHCP renews the reservation
    address, DHCP unfortunately can't update it on a renewal because it doesn't
    own the record. When you restart, it's a new, fresh lease. To make it work,
    you would need to add the DHCP server to the DnsUpdateProxy group. Read up
    on it ->

    How to configure DNS dynamic updates in Windows Server 2003 - scroll down to
    "Use the DnsUpdateProxy security group:"

    As for Revervations, they follow the lease period. Clients renew at 50%
    (half the lease time) and if not sucessful at 87.5% (7/8th of the lease
    time). This allows clients wil reservations to pick up updated DHCP options
    such as default gateway and DNS server information just like any other DHCP

    (scroll past the advertisements):

    The following is quoted from DHCP RFC 2131:

    2.2 Dynamic allocation of network addresses

    The second service provided by DHCP is the allocation of temporary or
    permanent network (IP) addresses to clients. The basic mechanism for
    the dynamic allocation of network addresses is simple: a client
    requests the use of an address for some period of time. The
    allocation mechanism (the collection of DHCP servers) guarantees not
    to reallocate that address within the requested time and attempts to
    return the same network address each time the client requests an
    address. In this document, the period over which a network address
    is allocated to a client is referred to as a "lease" [11]. The
    client may extend its lease with subsequent requests. The client may
    issue a message to release the address back to the server when the
    client no longer needs the address. The client may ask for a
    permanent assignment by asking for an infinite lease. Even when
    assigning "permanent" addresses, a server may choose to give out
    lengthy but non-infinite leases to allow detection of the fact that
    the client has been retired.


    This posting is provided "AS-IS" with no warranties or guarantees and
    confers no rights.

    Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT,
    MVP Microsoft MVP - Directory Services
    Microsoft Certified Trainer

    For urgent issues, you may want to contact Microsoft PSS directly. Please
    check http://support.microsoft.com for regional support phone numbers.

    Infinite Diversities in Infinite Combinations
    Ace Fekay [MVP], May 17, 2008
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  3. Ckuderna


    Jul 18, 2013
    Likes Received:
    Florence, AL
    Most likely both BOOTP and DHCP are enabled on the server, try turning off BOOTP either on the client or the server or both.

    BOOTP was the predecessor of DHCP. DHCP is based on the BOOTP protocol. They both use UDP ports 67 and 68.

    BOOTP does not have the concept of a lease and therefore the DHCP server can't give it one, so the DHCP server uses the BOOTP protocol to respond and therefore behaves as a BOOTP server, merely allocating an IP to a MAC; and with no lease concept, then it cannot expire the allocation and therefore shows it as infinite.

    You may be able to turn off the BOOTP option on the client so that it is forced to use DHCP, but this will require manual intervention for each client as you add them to the network.

    An alternative may be to disable BOOTP on the server side so that it refuses all BOOTP requests and forces the client to try any other IP allocation methods it may have, namely DHCP if it is (most likely) on.

    Leonard McCoy
    leomccoy, Jul 18, 2013
  4. Ckuderna


    Mar 22, 2015
    Likes Received:
    Try to turn off BOOTP...
    j_cocker, Mar 22, 2015
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