IP Class questionCompTIA Network+ Course

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This topic contains 3 replies, has 3 voices, and was last updated by  matthewbgage 3 years, 2 months ago.

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    So, Class A networks begin with 1 in the first octet (, etc.). What is a network with a zero in the first octet (0.x.x.x) classified as? I’ve seen that will be shown on some non-configured devices, but is it possible to have a valid network address such as

    I’m sorry if this is obvious but I haven’t been able to track down the answer on my own.


    Paul Rouk

    No, you will never see an IP address beginning with 0.x.x.x assigned to any device. IP addresses in that range are “reserved” and can’t actually be assigned or routed on the network.

    You might see them used during system initialization where is used as a placeholder for the system IP address until an actual address is assigned via DHCP.

    Wikipedia has a bit more on this topic.




    You state

    So, Class A networks begin with 1 in the first octet (, etc.).

    However I think this statement is incorrect. It would be more correct to say that a Class A network starts with a number between 1 and 126 in the first octet (1-



    This is what I thought, but I haven’t been able to find it documented any where. Did poke around on Wikipedia thanks to your link and found it mentioned that the subnet is reserved (https://en.wikipedia.org/wiki/IPv4#Special-use_addresses). That is the first mention I have found of this. The training videos, books, etc. just haven’t mentioned this, thought they will mentioned some of the other reserved ranges such as

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