192.168.10.0/24 - why /24 ? instead of 192.168.10/# notation query

Discussion in 'Windows Networking' started by Scott, Oct 15, 2008.

  1. Scott

    Scott Guest

    Please note the query below is about a LABEL in an ALPHANUMERIC field which
    could contain anything but its the example of a notation i dont understand.

    1Im looking at a hardware firewall to understand the layout of the rules.
    One of the destinations shows the address "name" field as: 192.168.10.0/24

    ("name" field is alpha numeric and is just a label).

    When i EDIT the NAME that hold the rule for the address, the actual numeric
    address is displayed as: 192.168.10.0/255.255.255.0

    I understand subnet 255.255.255.0 allows 256 IPs.

    So what im trying to get my head around is why "name" the destination
    192.168.10.0/24 as when i actaully edit the addrees its actually
    192.168.10.0/255.255.255.0.

    I understand this means allowing packet traffic incoming to 192.168.10.#.

    But why name it "192.168.10.0/24" ?

    Why not name it "192.168.10.#"

    I see this with several ISPs i use, they tend to add "IP/ number". Dont
    understand the /number notation means. Can someone explain ?

    Thank you.
     
    Scott, Oct 15, 2008
    #1
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  2. Scott

    Chris M Guest

    The /24 is the number of 'on' bits in the subnet mask.

    255.255.255.0, represented as octets in binary is:

    11111111.11111111.11111111.00000000

    Count the 1's :)
     
    Chris M, Oct 15, 2008
    #2
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  3. Scott

    JohnB Guest

    JohnB, Oct 15, 2008
    #3
  4. Scott

    Scott Guest

    The /24 is the number of 'on' bits in the subnet mask.

    Understood, simple now you mentiond it. So:

    192.168.10.0 / 24

    simply means:

    192.168.10.# / on subnet 255.255.255.0 / meaning 256 IP available on the
    subnet.

    Its just another way to display 255.255.255.0 without writing it !

    Thanks for the explaination guys :)
     
    Scott, Oct 16, 2008
    #4
  5. Scott

    Scott Guest

    thanks for the link too John.
     
    Scott, Oct 16, 2008
    #5
  6. Scott

    Chris M Guest

    No probs. While we're talking about it, remember that there won't be 256
    usable addresses:

    192.168.10.0 is the network ID

    192.168.10.255 is the subnet broadcast address
     
    Chris M, Oct 17, 2008
    #6
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