Question on Transcender Question :-)

Discussion in 'MCSE' started by eddiec, Apr 16, 2004.

  1. eddiec

    eddiec Guest

    I have a Win2K3 AD design transcender question in which you have two LANs
    connected by a WAN link. A requirement of the DHCP implementation is to
    provide redundancy in case of the failure of one server.

    Two possibile answers are:

    b) - Install a DHCP server in each office. On each server configure a single
    scope and an exclusion range.
    d) - Install a DHCP server in each office. On each server configure two
    scopes, for each scope configure an exclusion range.

    The recommended answer is (d). I do not understand this answer.

    Let's say that I have two subnets:

    LAN1 -
    LAN2 -

    connected by a WAN link.

    The DHCP server on LAN1 is set up to service DHCP requests from LAN2 as well
    as LAN1. Fine. But how will it know not to assign LAN2 IP addresses to local
    computers. If it does that the local computer will belong to the wrong
    subnet and will not be able to access any local resources?


    eddiec :)
    eddiec, Apr 16, 2004
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  2. eddiec

    Darth 2000 Guest

    Any relation to EddiePok/EddieRox?
    Darth 2000, Apr 16, 2004
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  3. This is the age-old eighty-twenty rule in action

    two subnets, two dhcp servers.
    Server on Subnet A
    subnet A 80% of address range
    subnet B 20% of address range

    Server on Subnet B
    subnet B 80% of address range
    subnet A 20% of address range

    Which means that if one server is down the other can temporarily issue
    new leases to give you time to recover - in reality this means a 4
    hour window to an 8 hour window to get things fixed with minimised
    impact on your environment.

    Your question on what addresses get assigned to which subnet is a good
    one. If your router is bootp/rfc1542 compliant then the discover
    broadcast from the other subnet will arrive at the dhcp server tagged
    with that fact in its header and the dhcp server will issue an address
    based on the route it took to get to the dhcp server.

    This means that server on subnet B *can* issue addresses for subnet A
    because the DORA has the correct tag information from the Subnet A
    interface of the router. Clever eh!!?

    My Hero:
    (remove vroomfondle to email me)
    Marlin Munrow, Apr 16, 2004
  4. eddiec

    Julian Guest

    Nice Info

    Julian, Apr 18, 2004
  5. eddiec

    zenner Guest

    Look at it from the other direction...why would you want local clients to
    get IP assignments over the links, from a distant source?

    It is much more logical to have local assignment of IP addresses. Cuts down
    on delay, overhead, frees up bandwidth...

    I can't believe that Transcender did not give a very lucid explanation to
    the question. Are you real sure you read it and looked up the references?
    You can't just use the simulation as a sole training aid. If you are really
    confused, Transcender does offer a help line/email contact.

    PS. Cross posting is usually discouraged. Instead of generating one thread,
    you are generating x times the number of post, plus those replies. It
    appears that Usenet bandwidth (traffic conservation) is a thing of the past,
    as are many other courtesies
    zenner, Apr 18, 2004
  6. eddiec

    Pieter Guest

    Look at it from the other direction...why would you want local clients to
    In general, you're right: IP addresses should be obtained locally as much as
    possible. The answer however lays in the question: you have to provide
    redundancy. In other words: you will set up the DHCP servers as described in
    answer D. As a result, computers will get their IP addresses locally, until
    that server fails or runs out of addresses.

    Best regards,

    P.s.: one of the courtesies you are talking about is not replying at the top
    of a posting, but at the bottom. Another one is quoting: deleting the parts
    of the message you are responding to that are not relevant. :)
    Pieter, Apr 24, 2004
  7. eddiec

    Zenner Guest

    I had to think about that. Since a large number of people do "top post" as
    you call it...

    I don't think you are right. If you read the original post (and subsequent
    replies) top posting allows you to read the reply without going through the
    entire history in each and every message. What you may be thinking about is
    "snipping" ... truncating the original message and/or previous replies.

    I hope you are not advocating cross posting?
    Zenner, May 20, 2004
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