CIDR Table – Basic Reference (From Wikipedia)

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Address Format Difference to last address Mask Addresses Relative to class Typical use
Decimal 2n A, B, C
a.b.c.d / 32 +0.0.0.0 255.255.255.255 1 20 ​1⁄256 C Host route
a.b.c.d / 31 +0.0.0.1 255.255.255.254 2 21 ​1⁄128 C Point to point links (RFC 3021)
a.b.c.d / 30 +0.0.0.3 255.255.255.252 4 22 ​1⁄64 C Point to point links (glue network)
a.b.c.d / 29 +0.0.0.7 255.255.255.248 8 23 ​1⁄32 C Smallest multi-host network
a.b.c.d / 28 +0.0.0.15 255.255.255.240 16 24 ​1⁄16 C Small LAN
a.b.c.d / 27 +0.0.0.31 255.255.255.224 32 25 ⅛ C
a.b.c.d / 26 +0.0.0.63 255.255.255.192 64 26 ¼ C
a.b.c.d / 25 +0.0.0.127 255.255.255.128 128 27 ½ C Large LAN
a.b.c.0 / 24 +0.0.0.255 255.255.255.0 256 28 1 C
a.b.c.0 / 23 +0.0.1.255 255.255.254.0 512 29 2 C
a.b.c.0 / 22 +0.0.3.255 255.255.252.0 1,024 210 4 C
a.b.c.0 / 21 +0.0.7.255 255.255.248.0 2,048 211 8 C Small ISP / large business
a.b.c.0 / 20 +0.0.15.255 255.255.240.0 4,096 212 16 C
a.b.c.0 / 19 +0.0.31.255 255.255.224.0 8,192 213 32 C ISP / large business
a.b.c.0 / 18 +0.0.63.255 255.255.192.0 16,384 214 64 C
a.b.c.0 / 17 +0.0.127.255 255.255.128.0 32,768 215 128 C
a.b.0.0 / 16 +0.0.255.255 255.255.0.0 65,536 216 256 C = B
a.b.0.0 / 15 +0.1.255.255 255.254.0.0 1,31,072 217 2 B
a.b.0.0 / 14 +0.3.255.255 255.252.0.0 2,62,144 218 4 B
a.b.0.0 / 13 +0.7.255.255 255.248.0.0 5,24,288 219 8 B
a.b.0.0 / 12 +0.15.255.255 255.240.0.0 10,48,576 220 16 B
a.b.0.0 / 11 +0.31.255.255 255.224.0.0 20,97,152 221 32 B
a.b.0.0 / 10 +0.63.255.255 255.192.0.0 41,94,304 222 64 B
a.b.0.0 / 9 +0.127.255.255 255.128.0.0 83,88,608 223 128 B
a.0.0.0 / 8 +0.255.255.255 255.0.0.0 1,67,77,216 224 256 B = A Largest IANA block allocation
a.0.0.0 / 7 +1.255.255.255 254.0.0.0 3,35,54,432 225 2:00 AM
a.0.0.0 / 6 +3.255.255.255 252.0.0.0 6,71,08,864 226 4:00 AM
a.0.0.0 / 5 +7.255.255.255 248.0.0.0 13,42,17,728 227 8:00 AM
a.0.0.0 / 4 +15.255.255.255 240.0.0.0 26,84,35,456 228 16 A
a.0.0.0 / 3 +31.255.255.255 224.0.0.0 53,68,70,912 229 32 A
a.0.0.0 / 2 +63.255.255.255 192.0.0.0 1,07,37,41,824 230 64 A
a.0.0.0 / 1 +127.255.255.255 128.0.0.0 2,14,74,83,648 231 128 A
0.0.0.0 / 0 +255.255.255.255 0.0.0.0 4,29,49,67,296 232 256 A

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