70-291 - question for the urber geeks

Discussion in 'MCSE' started by LMC, Oct 14, 2008.

  1. LMC

    LMC Guest

    There is the greatest likelihood that 70-291 could pose a question regarding
    sub-netting. The question is: “Does Microsoft recognize determining the
    valid number of subnets as “(2 squared by number of subnet bits) - 2“. It’s
    the 'subtract 2' part that I’m not sure about. According to Cisco you should
    Subtract 2 only if:

    1. You see “no ip subnet-zero†command in router configure.
    2. Routing protocol is classful ( RIP version 1 or IGRP )

    Now since Microsoft shows RIP as a choice WAN protocol I’m going to bet on
    the subtract 2. Any ideas? Any ideas where to direct the question perhaps?

    Honestly, I can’t wait for a response from the MCPGP guys. Its sarcastic
    Tuesday, let the harassment begin!!!
    LMC, Oct 14, 2008
    1. Advertisements

  2. LMC

    John R Guest

    Since every subnet has a network ID and a broadcast address, I believe the
    "-2" is correct.

    For example, if your LAN address is, that means the the
    network ID is, and the broadcast is You should
    not use these two addresses, therefore the number of useable addresses is
    254 (which would be 2**8 -2).

    Although many devices and network drivers support the use of the network ID
    as a valid useable address (especially if a NAT device is farther up the
    line), best practice is to never use it. The broadcast address also should
    never be used for a device.

    Personally, I believe that Cisco supports the use of it (the 'ip
    subnet-zero' option) because many ISPs are hurting for addresses and if they
    have a customer with a single router, they have to pare off a /31 subnet
    which is 4 addresses (the network ID, host router, customer router,
    broadcast address) which leaves no wiggle room. By supporting the use of
    the network ID as a valid address, another customer device can be added to a
    /31 network, instead of going to a /30 network (which would chew up even
    more addresses). That's just my take on it.

    For testing purposes, I went with the -2. Again, this is a Microsoft test,
    not a Cisco test.

    I'd offer some harassment, but I'm kind of lethargic today.

    John R
    John R, Oct 14, 2008
    1. Advertisements

  3. LMC

    John R Guest

    Ok, /30 and /29, not /31 and /30.
    John R, Oct 14, 2008
  4. LMC

    PAJ Guest

    Microsoft Certified Professional Group Policy?
    PAJ, Oct 14, 2008
  5. LMC

    CBIC Guest

    Actually according to Cisco you should subtract 2 unless you see ip subnet
    zero or using Rip ver.1 or IGRP
    CBIC, Oct 14, 2008
  6. Likelihood!? I can practically guarantee it! :)
    Well.... ironically... it was Microsoft who introduced the whole "forget
    about the -2" factor.

    And, the primary limitation was because RIP v1 and IGRP were written to
    conform to the RFCs.

    However, that 'requirement' has long since been abandoned, primarily as a
    result of the introduction of CIDR,
    and it's now common (theory, at least, if not practice) for the first and
    last subnets to be available for use.

    If you were working in an exclusively RIP v1 world, this would be a
    consideration. However, I doubt that you'd see such a "trick question".
    While you will see "trick questions", presenting an option to implement a .0
    subnet in a RIP v1 scenario probably isn't on the table. More significantly,
    though, should you be presented with such a question, my recommendation
    would be to eliminate all of the wrong answers first, and then work with the
    possible answers that are left.

    = = = = =
    Having said all of that, I just took at look at the MSPress MCSA/MSCE 70-291
    training kit, and on p2-27, the -2 factor is very well documented, so for
    purposes of the exam, I would likely go with the more stricter
    interpretation, which is that the first and last subnets are not available
    for use.
    = = = = =

    Lawrence Garvin, M.S., MCITP(x2), MCTS(x5), MCP(x7), MCBMSP
    Principal/CTO, Onsite Technology Solutions, Houston, Texas
    Microsoft MVP - Software Distribution (2005-2009)

    MS WSUS Website: http://www.microsoft.com/wsus
    My Websites: http://www.onsitechsolutions.com;
    My MVP Profile: http://mvp.support.microsoft.com/profile/Lawrence.Garvin
    Lawrence Garvin, Oct 14, 2008
  7. LMC

    LMC Guest

    Geez, is that the best you guys can do? Come on, I lost the price of a
    cadillac in the market last week.

    sheesh, how depressing ...
    LMC, Oct 14, 2008
  8. LMC

    PAJ Guest

    I am not "you guys". I am an individual. I don't have a clue what you
    are on about, neither I suspect do you.
    PAJ, Oct 14, 2008
  9. LMC

    CBIC Guest

    It wasn't a lame question. Do you want me to insult you for posting a well
    thought out question? OK-you have a bad haircut. Feel better now?
    CBIC, Oct 15, 2008
  10. LMC

    Frisbee® Guest

    I wish I had hair that could get cut.
    Frisbee®, Oct 15, 2008
  11. LMC

    PAJ Guest

    It is not nice to mock the afflicted.
    PAJ, Oct 16, 2008
  12. LMC

    LMC Guest

    Ah, now that's what I've become accustom too. It's going to be a good week
    after all...
    LMC, Oct 20, 2008
  13. LMC

    Andrew Du Guest

    I think you will find there will be a clue in the question.

    Generally you'll see something like "you are using Cisco routers" in the
    question text, so that's a clue that MS want you to think the Cisco way for
    that one.
    Andrew Du, Oct 29, 2008
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.