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As per title, bit also what do different numbers mean?

I don't know what the name is of that number - feel free to improve the title.

Bohemian
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  • The `24` is the *netmask* in *CIDR notation*, which is to say, the number of left-most bits that define the network portion of an IPv4 address. The remaining right-most bits (32-24=8, in this case) are the host portion of the address. – user4556274 Jan 10 '17 at 17:43
  • Here's a Wikipedia article that explains it pretty well: https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing – Charles Burge Jan 10 '17 at 17:46
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    I'm wondering why this question is being downvoted. Just because I don't know something "obvious" doesn't mean it's a bad question. You try googling for "24" and see how far it gets you to an answer. – Bohemian Jan 10 '17 at 17:56

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The address you give is in what is called "Classless Internet Domain Routing" format, or sometimes "supernetting". Originally, internet addresses were allocated in fixed-size blocks, and the size of the block and the first few bits of the block's address defined the class. In 1993, because of improvements in technology and a perceived need for smaller and more varied block sizes (because IP addresses were being used at a rapid rate), the Class-based allocation (described at https://en.wikipedia.org/wiki/Classful_network) was replaced by the current Classless allocation (described at https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing).

The number before the slash (255.255.0.0 in your example in the title) is an address or a netmask; the number after the slash (/24, in your example) defines the block via the netmask - in other words, your title defines a net block of 256 addresses in the range 255.255.0.0 through 255.255.0.255 - the first 24 bits define the constant part of the block, and the remainder can vary per device.

Both numbers are important; if you had written (for example) 10.4.0.0/16, the block defined would be much larger, varying from 10.4.0.0 to 10.4.255.255, since only 16 bits would be defining the constant part of the block. The two links give a much better explanation than I can.

Jeff Zeitlin
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