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  • Category: Computers

    Why do we need Subnet mask?

    Why do we need to give the subnet mask when configuring the IP address on my computer? I am using my PC at my home and I am not having any other subnets. I understand that I need subnet mask to identify between subnets but that is not the case here. Please reply.
  • #3897

    Nice Question. Definitely subnetmask is needed for identify different subnets.
    In the Question you do not mention which type of internet connection you have used at your home. For Internet connection purpose, most cases you need not have to give the subnet mask seperately. for that purpose just check the "obtain ip automatically". Your service provider will give you an ip address for communicating through internet.

    That is not the case you have a LAN in your home. That means, if you create a LAN in Home. You can share datas, internet etc within the computers connected to that LAN. In such cases, You have to provide seperate Private IP addresses to all computers connected to LAN and must have to define subnet mask there.

    Sameera M

  • #3900
    Hi Sameera,

    Thanks for your reply. However I don't think you have given me the answer to my question. I know that I need to give the subnet mask when we configure the IP address but what I want to know is that why do we have to?

    Even if you configure your computer to gain the IP address automatically it still gets the subnetmask. Eventhough that is being provided automatically by the ISP.

    I can understand the necessity of the subnetmask when we are connecting to the Internet, but what if I am not? What if I am just having few computers locally without accessing the internet and communicating among themselves. It is a single flat network and there are no subnets involved. So then why do you need a subnetmask then?

  • #3920
    Network Protocol is a set of rules which instruct the devices which are connected to a network, how to communicate each other.

    TCP/IP (Transmission Control Protocol / Internet Protocol) is a network protocol which used for internetwork. This can also be used for LAN. In a network, which uses tcp/ip (Transmission Control Protocol / Internet Protocol), Internet Protocol Address is a must. The IP address is used for identifying the network device connected to a network. All the Device Connected to a network must have a ip address.

    The Subnet mask is an unavoidable part of the IP Address, which tells the network that the device is from which subnet. The IP address and subnet mask do not have independent existence. As we know internet is a network of networks. There are various subnets in that network. If we are using the TCP/IP for local area network, which do not have even sub network, it automatically assigns certain level of hierarchy. So subnet mask is a must in the network you have mentioned.

  • #3960
    MS Rajalekshmi has already explained that TCP/IP (Transmission Control Protocol / Internet Protocol) is a network protocol which used for internetwork.

    A subnet also known as sub net work or sub division of an IP (Internet protocol) network is separate part of an organisation's network which can be identified. The sub netting /sub division is essential when one net work number has to be distributed over more than one LAN (local area network).

    An IP address has 2 components – 1. The network address and 2. The host addresses. The subnet mask defines which portion of the IP address belongs to host computer and which portion belongs to the network. This in turn will help to know whether the data is going to the correct computer on the correct network.

    With Regards
    Ramanathan A R

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