class C network with class B subnet mask question

Discussion in 'Cisco' started by jonnah, May 18, 2004.

  1. jonnah

    jonnah Guest

    Hi,

    What will happen if we use a class B subnet mask (255.255.0.0) on a
    class C network such as (192.168.0.0)?


    Thanks
    jonnah, May 18, 2004
    #1
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  2. jonnah

    KR Guest

    jonnah wrote:
    > Hi,
    >
    > What will happen if we use a class B subnet mask (255.255.0.0) on a
    > class C network such as (192.168.0.0)?
    >


    Nothing. The concept of "classes" really went out the window when CIDR
    was introduced. You may have to use the "ip classless" command. Your
    question was Cisco related, I assume?
    KR, May 18, 2004
    #2
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  3. jonnah

    Hansang Bae Guest

    In article <>, jonnah888
    @yahoo.com says...
    > Hi,
    >
    > What will happen if we use a class B subnet mask (255.255.0.0) on a
    > class C network such as (192.168.0.0)?


    The network will blow up.

    Nothing will happen. We now live in a CIDR world and classful mask
    restrictions is a thing of the past. Unless you have WFWG in your
    network, you'll be fine.


    --

    hsb

    "Somehow I imagined this experience would be more rewarding" Calvin
    *************** USE ROT13 TO SEE MY EMAIL ADDRESS ****************
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    Hansang Bae, May 18, 2004
    #3
  4. In article <>,
    (jonnah) wrote:

    > Hi,
    >
    > What will happen if we use a class B subnet mask (255.255.0.0) on a
    > class C network such as (192.168.0.0)?


    This is called "supernetting" or "aggregation". It will treat the block
    of networks as a single network for routing purposes.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
    Barry Margolin, May 18, 2004
    #4
  5. jonnah

    jonnah Guest

    Barry Margolin <> wrote in message news:<>...
    > In article <>,
    > (jonnah) wrote:
    >
    > > Hi,
    > >
    > > What will happen if we use a class B subnet mask (255.255.0.0) on a
    > > class C network such as (192.168.0.0)?

    >
    > This is called "supernetting" or "aggregation". It will treat the block
    > of networks as a single network for routing purposes.


    So my 192.168.0.0/24 network will essentially have 512 subnets with
    65534 hosts per subnet using a /16 subnet mask?
    jonnah, May 19, 2004
    #5
  6. In article <>,
    jonnah <> wrote:
    :Barry Margolin <> wrote in message news:<>...
    :> In article <>,
    :> (jonnah) wrote:
    :> > What will happen if we use a class B subnet mask (255.255.0.0) on a
    :> > class C network such as (192.168.0.0)?

    :> This is called "supernetting" or "aggregation". It will treat the block
    :> of networks as a single network for routing purposes.

    :So my 192.168.0.0/24 network will essentially have 512 subnets with
    :65534 hosts per subnet using a /16 subnet mask?

    No, if you configure your hosts as 192.168.0.0/16 then your
    base reverved address will be 192.168.0.0, your broadcast address
    will be 192.168.255.255, and everything else will be usable host space.
    As long, that is, as all the other equipment involved agrees on it
    being /16. You would, for example, run into trouble if you tried
    to use RIP1 with this.

    If you configure "ip classless" then you do not even have to worry
    about "ip subnet-zero". CIDR does not reserve the first and last
    subnets.
    --
    Will you ask your master if he wants to join my court at Camelot?!
    Walter Roberson, May 19, 2004
    #6
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