Network – just to remember

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IPv4 CIDR
Address
format
Difference
to last address
Mask Addresses Relative
to class
A, B, C
Restrictions Typical use
Decimal 2n
a.b.c.d/32 +0.0.0.0 255.255.255.255 1 20 1256 C Host route
a.b.c.d/31 +0.0.0.1 255.255.255.254 2 21 1128 C d = 0 … (2n) … 254 Point to point links (RFC 3021)
a.b.c.d/30 +0.0.0.3 255.255.255.252 4 22 164 C d = 0 … (4n) … 252 Point to point links (glue network)
a.b.c.d/29 +0.0.0.7 255.255.255.248 8 23 132 C d = 0 … (8n) … 248 Smallest multi-host network
a.b.c.d/28 +0.0.0.15 255.255.255.240 16 24 116 C d = 0 … (16n) … 240 Small LAN
a.b.c.d/27 +0.0.0.31 255.255.255.224 32 25 ⅛ C d = 0 … (32n) … 224
a.b.c.d/26 +0.0.0.63 255.255.255.192 64 26 ¼ C d = 0, 64, 128, 192
a.b.c.d/25 +0.0.0.127 255.255.255.128 128 27 ½ C d = 0, 128 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 c = 0 … (2n) … 254
a.b.c.0/22 +0.0.3.255 255.255.252.0 1,024 210 4 C c = 0 … (4n) … 252 Small business
a.b.c.0/21 +0.0.7.255 255.255.248.0 2,048 211 8 C c = 0 … (8n) … 248 Small ISP/ large business
a.b.c.0/20 +0.0.15.255 255.255.240.0 4,096 212 16 C c = 0 … (16n) … 240
a.b.c.0/19 +0.0.31.255 255.255.224.0 8,192 213 32 C c = 0 … (32n) … 224 ISP/ large business
a.b.c.0/18 +0.0.63.255 255.255.192.0 16,384 214 64 C c = 0, 64, 128, 192
a.b.c.0/17 +0.0.127.255 255.255.128.0 32,768 215 128 C c = 0, 128
a.b.0.0/16 +0.0.255.255 255.255.0.0 65,536 216 256 C = B
a.b.0.0/15 +0.1.255.255 255.254.0.0 131,072 217 2 B b = 0 … (2n) … 254
a.b.0.0/14 +0.3.255.255 255.252.0.0 262,144 218 4 B b = 0 … (4n) … 252
a.b.0.0/13 +0.7.255.255 255.248.0.0 524,288 219 8 B b = 0 … (8n) … 248
a.b.0.0/12 +0.15.255.255 255.240.0.0 1,048,576 220 16 B b = 0 … (16n) … 240
a.b.0.0/11 +0.31.255.255 255.224.0.0 2,097,152 221 32 B b = 0 … (32n) … 224
a.b.0.0/10 +0.63.255.255 255.192.0.0 4,194,304 222 64 B b = 0, 64, 128, 192
a.b.0.0/9 +0.127.255.255 255.128.0.0 8,388,608 223 128 B b = 0, 128
a.0.0.0/8 +0.255.255.255 255.0.0.0 16,777,216 224 256 B = A Largest IANA block allocation
a.0.0.0/7 +1.255.255.255 254.0.0.0 33,554,432 225 2 A a = 0 … (2n) … 254
a.0.0.0/6 +3.255.255.255 252.0.0.0 67,108,864 226 4 A a = 0 … (4n) … 252
a.0.0.0/5 +7.255.255.255 248.0.0.0 134,217,728 227 8 A a = 0 … (8n) … 248
a.0.0.0/4 +15.255.255.255 240.0.0.0 268,435,456 228 16 A a = 0 … (16n) … 240
a.0.0.0/3 +31.255.255.255 224.0.0.0 536,870,912 229 32 A a = 0 … (32n) … 224
a.0.0.0/2 +63.255.255.255 192.0.0.0 1,073,741,824 230 64 A a = 0, 64, 128, 192
a.0.0.0/1 +127.255.255.255 128.0.0.0 2,147,483,648 231 128 A a = 0, 128
0.0.0.0/0 +255.255.255.255 0.0.0.0 4,294,967,296 232 256 A

In common usage

 

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