Network Masks

Discussion in 'Home Networking' started by Geoff Lane, Oct 19, 2005.

  1. Geoff Lane

    Geoff Lane Guest

    Network masks are confusing me a wee bit.

    I think I understand that 192.168.1.1/255.255.255.255 refers to the
    specific address of 192.168.1.1

    192.168.1.0/255.255.255.0 I think refers to the entire range from
    192.168.1.0 to 192.168.1.255 so can the preceeding IP address actually
    be anything in the 192.168.1 range?

    Now with a filter of 255.255.255.252 I think this gives a range of 4
    IP addresses, I'm thinking, if the address was given as
    192.168.1.254/255.255.255.252 what addresses would be covered?

    Geoff Lane
     
    Geoff Lane, Oct 19, 2005
    #1
    1. Advertisements

  2. Geoff Lane wrote in message
    :
    Yes, except 192.168.1.0 and 192.168.1.255 which are reserved for broadcast
    and multicast addresses.

    I think it's convention to express a subnet by referring to the lowest value
    in the range, rather than an arbitrary address within the range - so it
    would normally be stated as 192.168.1.252/255.255.255.252 or
    192.168.1.252/30 (30 = number of 1s in subnet mask), covering addresses 252,
    253, 254 and 254. I think 252 and 255 would be reserved for broadcast,
    leaving you with just two usable addresses.
     
    Martin Underwood, Oct 19, 2005
    #2
    1. Advertisements

  3. Geoff Lane

    Geoff Lane Guest

    Thanks for quick reply, I'm slowly getting there :)))

    I understand about the reserved addresses within ranges so your
    explanation was helpful.

    Geoff Lane
     
    Geoff Lane, Oct 19, 2005
    #3
  4. Geoff Lane

    Adam Piggott Guest

    -----BEGIN PGP SIGNED MESSAGE-----
    Hash: SHA1

    I've found this site useful in the past (and present):

    IP Address Subnetting Tutorial, Ralph Becker
    http://www.ralphb.net/IPSubnet/index.html

    HTH
    - --
    Adam Piggott, Proprietor, Proactive Services (Computing).
    http://www.proactiveservices.co.uk/

    Please replace dot invalid with dot uk to email me.
    Apply personally for PGP public key.
    -----BEGIN PGP SIGNATURE-----
    Version: GnuPG v1.4.2 (MingW32)

    iD8DBQFDVrxz7uRVdtPsXDkRAkoCAKCWrefL6JNDyCZfW42iWqTQKgKkvACeIEsW
    l3tybAcFGPZy32o78iPYjAU=
    =ORSX
    -----END PGP SIGNATURE-----
     
    Adam Piggott, Oct 19, 2005
    #4
  5. Geoff Lane

    Alex Fraser Guest

    The lowest address in the range is called the network address. The highest
    is the subnet broadcast address. As you wrote, both these addresses are
    reserved (though I think the reasons are mostly/entirely historical in the
    former case). Multicast is an entirely different kettle of fish; multicast
    addresses are in 224.0.0.0/4.

    Alex
     
    Alex Fraser, Oct 19, 2005
    #5
  6. Alex Fraser wrote in
    :
    I was nearly right! I should have realised that broadcasting (to all
    computers within the subnet) would use an address within the subnet but
    multicasting (to all computers on the network segment, irrespective of
    subnet) would use a special subnet.
     
    Martin Underwood, Oct 19, 2005
    #6
  7. Geoff Lane

    Clint Sharp Guest

    If you have broadband, you might like http://www.howtosubnet.com

    I worked out subnet masks by imagining them as a ruler, you cover the
    TCP/IP address with the ruler until you can't see any more of the bits
    of the subnet mask and then any bits still showing of the IP address are
    the network. I guess that works best if you realise the binary of the
    address.
     
    Clint Sharp, Oct 20, 2005
    #7
  8. Geoff Lane

    Clint Sharp Guest

    Bugger, posting at 25 to 1 in the morning is not generally conducive to
    accuracy, I should have said;
    and then any bits still showing of the IP address are the host range
    minus the broadcast and network addresses.
     
    Clint Sharp, Oct 20, 2005
    #8
  9. Geoff Lane

    Alex Fraser Guest

    If you understand binary and boolean logic, then it is a small step to grasp
    the idea of bitwise logical operations, and with that pretty much everything
    related to subnet masks should be trivial.

    Alex
     
    Alex Fraser, Oct 21, 2005
    #9
    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.