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IPv4 Subnet Cheatsheet

CIDR

Subnet Mask

Total IPs

Usable IPs

/32 255.255.255.255 1 1
/31 255.255.255.254 2 2*
/30 255.255.255.252 4 2
/29 255.255.255.248 8 6
/28 255.255.255.240 16 14
/27 255.255.255.224 32 30
/26 255.255.255.192 64 62
/25 255.255.255.128 128 126
/24 255.255.255.0 256 254
/23 255.255.254.0 512 510
/22 255.255.252.0 1024 1022
/21 255.255.248.0 2048 2046
/20 255.255.240.0 4096 4094
/19 255.255.224.0 8192 8190
/18 255.255.192.0 16,384 16,382
/17 255.255.128.0 32,768 32,766
/16 255.255.0.0 65,536 65,534
/15 255.254.0.0 131,072 131,070
/14 255.252.0.0 262,144 262,142
/13 255.248.0.0 524,288 524,286
/12 255.240.0.0 1,048,576 1,048,574
/11 255.224.0.0 2,097,152 2,097,150
/10 255.192.0.0 4,194,304 4,194,302
/9 255.128.0.0 8,388,608 8,388,606
/8 255.0.0.0 16,777,216 16,777,214
/7 254.0.0.0 33,554,432 33,554,430
/6 252.0.0.0 67,108,864 67,108,862
/5 248.0.0.0 134,217,728 134,217,726
/4 240.0.0.0 268,435,456 268,435,454
/3 224.0.0.0 536,870,912 536,870,910
/2 192.0.0.0 1,073,741,824 1,073,741,822
/1 128.0.0.0 2,147,483,648 2,147,483,646

*See rfc 3021

Private IP ranges

Class Size Subnet Mask Range of IPs
Class A 10.0.0.0/8 255.0.0.0 10.0.0.0 - 10.255.255.255
Class B 172.16.0.0/12 255.240.0.0 172.16.0.0 - 172.31.255.255
Class C 192.168.0.0/16 255.255.0.0 192.168.0.0 - 192.168.255.255

IPv6

Prefix

/48s

/56s

/64s

/24 16M 4G 1T
/25 8M 2G 512G
/26 4M 1G 256G
/27 2M 512M 128G
/28 1M 256M 64G
/29 512K 128M 32G
/30 256K 64M 16G
/31 128K 32M 8G
/32 64K 16M 4G
/33 32K 8M 2G
/34 16K 4M 1G
/35 8K 2M 512M
/36 4K 1M 256M
/37 2K 512K 128M
/38 1K 256K 64M
/39 512 128K 32M
/40 256 64K 16M
/41 128 32K 8M
/42 64 16K 4M
/43 32 8K 2M
/44 16 4K 1M
/45 8 2K 512K
/46 4 1K 256K
/47 2 512 128K
/48 1 256 64K
/49 128 32K
/50 64 16K
/51 32 8K
/52 16 4K
/53 8 2K
/54 4 1K
/55 2 512
/56 1 256
/57 128
/58 64
/59 32
/60 16
/61 8
/62 4
/63 2
/64 1

IPv6 bit mapping

XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX
      ||| |||| |||| |||| |||| |||| ||||
      ||| |||| |||| |||| |||| |||| |||128
      ||| |||| |||| |||| |||| |||| ||124
      ||| |||| |||| |||| |||| |||| |120
      ||| |||| |||| |||| |||| |||| 116
      ||| |||| |||| |||| |||| |||112
      ||| |||| |||| |||| |||| ||108
      ||| |||| |||| |||| |||| |104
      ||| |||| |||| |||| |||| 100
      ||| |||| |||| |||| |||96
      ||| |||| |||| |||| ||92
      ||| |||| |||| |||| |88
      ||| |||| |||| |||| 84
      ||| |||| |||| |||80
      ||| |||| |||| ||76
      ||| |||| |||| |72
      ||| |||| |||| 68
      ||| |||| |||64
      ||| |||| ||60
      ||| |||| |56
      ||| |||| 52
      ||| |||48
      ||| ||44
      ||| |40
      ||| 36
      ||32
      |28
      24

Binary

Bit 1 1 1 1 1 1 1 1
Bit Value 128 64 32 16 8 4 2 1

An IP calculator may be more useful.
You will learn all this by simply practicing subnetting

Feel free to print or save the following IPv4 and IPv6 cheat sheets:
IPv4 Subnetting Cheat Sheet IPv6 Subnetting Cheat Sheet
OSI, TCP/IP layer Cheat Sheet

If you are studying for the CCNA, you may also be interested in mastering your IPv4 and IPv6 header information and a good CCNA book .

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