what is difference between Public IP and Private IP

Posted on 2008-11-18
Last Modified: 2012-06-27
Dear EE,

I'm aware that public IP is used to connect to the internet world and private IP are used within our local LAN so that its protected from external world.
I have 3 systems in LAN, as I want to use for internal purpose I should use private IP, but as i took internet connection he has given me IP and I m using those. (They are class c Private IP's. Can I use class A private IP's.)
Also Iwan to know what the other attributes are Subnet mask, Default Gate way, Preferred DNS, Alternate DNS
Question by:agcps
    LVL 10

    Expert Comment

    You are correct about the Public IP address linking the internet portion to the local. No, unless you have multiple public address's (rare) you should stick to private IP's locally.
    The subnet mask can be changed and there are many settings for many reasons. One is to allow multiple Private IP ranges to communicate. One example is a subnet mask of could allow up to for ranges of Private IP's to communicate, such as -
    The DNS settings are Domain Name Systems. The address you point to here(must be valid) says that the target address can convert address's like to thier relative Public IP address, ex  An alternate can be used if you are running through a Server, you can set the Primary as the Server so it will look locally first, then to the alternative.
    Hope this helps!  - It is a deep subject, I just touched the surface...
    LVL 10

    Expert Comment

    Wikipedia for the different entries can help you learn more of the capabilities of each piece and how they relate...
    I would go in to more detail but sites like Wikipedia can show you in far more depth and with examples etc.
    LVL 3

    Accepted Solution

    Not sure what your first question is exactly could you clarify?

    But as for "Also Iwan to know what the other attributes are Subnet mask, Default Gate way, Preferred DNS, Alternate DNS" I'll do my best

    Subnet Mask: This basically tells your computer what group of IP address your computer is a part of... means your computers is on a group that ranges from to

    Default Gately: Is usually a router that is specified  that your Computer needs to communicate through to get to any other netword or subnet.

    Preffered DNS server: Is the address of a server your computer will communicate with to convert a URL (web address) to a number (IP address) so your computer can understand (Computers understand numbers and need web address converted)

    Alternate DNS server: Is just another server that you computer will try to contact if the Preffered DNS server can't help you
    LVL 3

    Expert Comment

    you can use another class of IP Addresses. however it seems the gateway addr provided to you is pointing to some device the ISP installed at your premises. would require details of how you are setup i.e. whether its a direct Lan cable/ Phone cable or something else. Try opening & check whether a page or login screen is displayed. if are probably using a router ...then you might need to verify with the router vendor supports changing of IP address pool...
    LVL 3

    Expert Comment

    You can use Class A private network ( if you want

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