User:ToBeFree/CIDR
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CIDR notation for IP addresses.
IPv4[edit]
The number after the slash is the number of bits that you are specifically referring to. For example, if you are specifically referring to one IP address, you can write "/32", as you are referring to all of the 32 bits an IPv4 address has. If you are referring to all IP addresses in the world, you can write "/0", as you are not referring to anything in specific.
- "1.0.0.0/8" is every IP address that starts with "1."
- "1.1.0.0/16" is every IP address that starts with "1.1."
- "1.1.1.0/24" is every IP address that starts with "1.1.1.". That's 256 addresses.
- "1.1.1.0/25" begins at "1.1.1.0" and ends at the half of the next block, "1.1.1.127". That's 128 addresses. You can halve that block further:
- "1.1.1.0/26" begins at "1.1.1.0" and ends at "1.1.1.63". That's 64 addresses. And once more:
- "1.1.1.0/27" begins at "1.1.1.0" and ends at "1.1.1.31". That's 32 addresses.
IPv6[edit]
The number after the slash says how much of the left side you refer to. Each block separated by colons has a size of 16 (bits). If you mean all addresses that start with "2601:342:c003:3f0", you mean four of these blocks. That's 16*4=64.
Almost always, 64 is the highest meaningful number you'll see, as almost every internet connection is allowed to use an entire /64 for themselves. So if you want to calculate a range, you can use the IP range calculator (IPv6) but if your result has a larger number than "64" at the end, replace it by 64.