subnet mask - TCP-IP

This is a discussion on subnet mask - TCP-IP ; In article , Barry Margolin wrote: >> It's an actual question from Microsoft 70-291 exam. > >You keep saying that as if "70-291" is supposed to mean something to us. "Impress us" might be more accurate than "mean something to ...

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Thread: subnet mask

  1. Re: subnet mask

    In article ,
    Barry Margolin wrote:

    >> It's an actual question from Microsoft 70-291 exam.

    >
    >You keep saying that as if "70-291" is supposed to mean something to us.


    "Impress us" might be more accurate than "mean something to us."
    http://www.google.com/search?q=70-291 might have clues about it. One hit is
    http://www.microsoft.com/learning/en...ms/70-291.mspx
    which says in part:

    The Microsoft Certified Systems Administrator (MCSA) on Windows
    Server 2003 credential is intended for IT professionals who
    work in the typically complex computing environment of medium
    to large companies. An MCSA candidate should have 6 to 12 months
    of experience administering client and network operating systems
    in environments that have the following characteristics:

    250 to 5,000 or more users

    Three or more physical locations

    Three or more domain controllers

    Network services and resources such as messaging, database,
    file and print, proxy server, firewall, Internet, intranet,
    remote access, and client computer management

    Connectivity requirements such as connecting branch offices and
    individual users in remote locations to the corporate network
    and connecting corporate networks to the Internet

    (heavy sigh)


    Vernon Schryver vjs@rhyolite.com

  2. Re: subnet mask

    On 2008-07-04 20:24:29 -0400, "eager" said:

    > Barry,
    >
    > The DHCP server in subnet A is to lease IP addresses to 5 Client computers
    > in Subnet A.
    > The server in subnet B offers services to 5 clients in subnet A.
    >
    > I totally agree, this does not make any sense to me, that's why I posted it
    > here.
    > It's an actual question from Microsoft 70-291 exam.



    While this may sound troll-ish, I have to chime in here with this.
    Considering that Micro$oft has the worst-performing TCP/IP stack, and
    the one that is the most non-RFC compliant, I'm not surprised bogus,
    misleading, or garbage questions make it into their exams. I've spent a
    significant amount of my career trying to manage, contain or obviate
    the trash Microsoft produces when data is washed through one of their
    OS's.

    Eager, the world is not Microsoft, it's an ecosystem of many, many
    different things. When you can't get a result with one tool, you might
    try getting a result on different tools and comparing the differences.
    This is an important troubleshooting skill I had to cultivate long ago
    for myself. If it's broke on this OS, I try it on that OS to check my
    results and my troubleshooting path.

    I'm going to break down your example with some notes and see if I can
    make sense of this:

    > 5 Client computers in Subnet A:
    > IP address: 10.10.10.66 - 10.10.10.70
    > Subnet mask: 255.255.255.192
    > Default gateway: 10.10.10.65


    IP subnet masks are not to be applied to arbitrary ranges - you can't
    "pick a range" and then apply a subnet mask to it - it's mathematical
    based chunking of IP addresses - I'll avoid a lengthy discussion here
    on this, since it's in a ton of books, but the network you specify
    above is actually this one, regardless of the range of IP addresses
    specified. The IP addresses 10.10.10.66-10.10.10.70 with a netmask of
    255.255.255.192 fall into this range:

    Network Range : 10.10.10.64 - 10.10.10.127
    Network Address : 10.10.10.64 (reserved)
    Network Broadcast : 10.10.10.127 (reserved)

    The default gateway you list isn't a convention, there's a traditional
    sense that the first usable IP address, in this case 10.10.10.65
    usually is used as the default router, and sometimes the "highest"
    usable IP address, such as 10.10.10.126, could be a DNS server. If you
    set a host with 10.10.10.66, for example, with a netmask of
    255.255.255.192, it will expect that the non-reserved addresses in the
    range are local to it and do not need a router. This means that the
    host @ 10.10.10.66 thinks it doesn't need a router for any address
    between 10.10.10.64 & 10.10.10.127

    > Server in Subnet B:
    > IP address: 10.10.10.94
    > Subnet mask: 255.255.255.240
    > Default gateway: 10.10.10.93


    Network Range : 10.10.10.80 - 10.10.10.95
    Network Address : 10.10.10.80 (reserved)
    Network Broadcast : 10.10.10.95 (reserved)

    A host with an address of 10.10.10.94 will expect that non-reserved
    addresses are local to it.

    Let's look at a sample conversation, the DHCP server is not relevant to
    the question at all, actually.

    The clients in Subnet A, all think, by the netmask set, that the
    addresses you have in Subnet B are local to them, so they will never
    contact a router to forward the packet. Since the addresses you have in
    Subnet B are already a part of what is in Subnet A, the host has no
    reason to go to the router to forward packets. It will simply ARP for
    the address and fail unless, like another poster said, Proxy-ARP is
    used.

    In a real-world configuration, this setup is defective and would need
    correction. Overlapping subnet definitions in a network are rarely if
    ever used in real-world deployments.

    Changing the netmask on the other subnet to 255.255.255.192 would
    create two subnets that are identical to each other. In Microsoft's
    world, perhaps this turns on Proxy-ARP or something if you actually
    configure this on one of their operating systems, and then it just
    works. Cisco routers would barf at this and tell you that you're trying
    to define the same subnet twice, without a special configuration type.

    This question is probably trying to test a grasp of subnet masking and
    a minor amount of RFC-based router functionality.

    /dmfh


    --
    _ __ _
    __| |_ __ / _| |_ 01100100 01101101
    / _` | ' \| _| ' \ 01100110 01101000
    \__,_|_|_|_|_| |_||_| dmfh(-2)dmfh.cx


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