CIDER:Classless Inter-Domain Routing http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing

IP/CIDR
Δ to last IP addr
Mask
No of Hosts
start ip address
stop ip address
Class
Notes
a.b.c.d/32 +0.0.0.0 255.255.255.255 1 a.b.c.0 a.b.c.0 1/256 C  
a.b.c.d/31 +0.0.0.1 255.255.255.254 2 a.b.c.0 a.b.c.1 1/128 C d = 0 ... (2n) ... 254
a.b.c.d/30 +0.0.0.3 255.255.255.252 4 a.b.c.0 a.b.c.3 1/64 C d = 0 ... (4n) ... 252
a.b.c.d/29 +0.0.0.7 255.255.255.248 8 a.b.c.0 a.b.c.7 1/32 C d = 0 ... (8n) ... 248
a.b.c.d/28 +0.0.0.15 255.255.255.240 16 a.b.c.0 a.b.c.15 1/16 C d = 0 ... (16n) ... 240
a.b.c.d/27 +0.0.0.31 255.255.255.224 32 a.b.c.0 a.b.c.31 1/8 C d = 0 ... (32n) ... 224
a.b.c.d/26 +0.0.0.63 255.255.255.192 64 a.b.c.0 (64,128,192) a.b.c.63(127,191,255) 1/4 C d = 0, 64, 128, 192
a.b.c.d/25 +0.0.0.127 255.255.255.128 128 a.b.c.0 (128) a.b.c.127 (255) 1/2 C d = 0, 128
a.b.c.0/24 +0.0.0.255 255.255.255.000 256 a.b.c.0 a.b.c.255 1 C  
a.b.c.0/23 +0.0.1.255 255.255.254.000 512 a.b.0.0 a.b.1.255 2 C c = 0 ... (2n) ... 254
a.b.c.0/22 +0.0.3.255 255.255.252.000 1,024 a.b.0.0 a.b.3.255 4 C c = 0 ... (4n) ... 252
a.b.c.0/21 +0.0.7.255 255.255.248.000 2,048 a.b.0.0 a.b.7.255 8 C c = 0 ... (8n) ... 248
a.b.c.0/20 +0.0.15.255 255.255.240.000 4,096 a.b.0.0 a.b.15.255 16 C c = 0 ... (16n) ... 240
a.b.c.0/19 +0.0.31.255 255.255.224.000 8,192 a.b.0.0 a.b.31.255 32 C c = 0 ... (32n) ... 224
a.b.c.0/18 +0.0.63.255 255.255.192.000 16,384 a.b.0 (64,128,192).0 a.b.63 (127,191, 255).255 64 C c = 0, 64, 128, 192
a.b.c.0/17 +0.0.127.255 255.255.128.000 32,768 a.b.0 (128).0 a.b.127 (255).255 128 C c = 0, 128
a.b.0.0/16 +0.0.255.255 255.255.000.000 65,536 a.b.0.0 a.b.255.255 256 C = 1 B  
a.b.0.0/15 +0.1.255.255 255.254.000.000 131,072 a.0.0.0 a.1.255.255 2 B b = 0 ... (2n) ... 254
a.b.0.0/14 +0.3.255.255 255.252.000.000 262,144 a.0.0.0 a.3.255.255 4 B b = 0 ... (4n) ... 252
a.b.0.0/13 +0.7.255.255 255.248.000.000 524,288 a.0.0.0 a.7.255.255 8 B b = 0 ... (8n) ... 248
a.b.0.0/12 +0.15.255.255 255.240.000.000 1,048,576 a.0.0.0 a.15.255.255 16 B b = 0 ... (16n) ... 240
a.b.0.0/11 +0.31.255.255 255.224.000.000 2,097,152 a.0.0.0 a.31.255.255 32 B b = 0 ... (32n) ... 224
a.b.0.0/10 +0.63.255.255 255.192.000.000 4,194,304 a.0.0.0 a.63.255.255 64 B b = 0, 64, 128, 192
a.b.0.0/9 +0.127.255.255 255.128.000.000 8,388,608 a.0 (128).0.0 a.127(255).255.255 128 B b = 0, 128
a.0.0.0/8 +0.255.255.255 255.000.000.000 16,777,216 a.0.0.0 a.255.255.255 256 B = 1 A  
a.0.0.0/7 +1.255.255.255 254.000.000.000 33,554,432 0.0.0.0 1.255.255.255
2A
a = 0 ... (2n) ... 254
a.0.0.0/6 +3.255.255.255 252.000.000.000 67,108,864 0.0.0.0 3.255.255.255
4A
a = 0 ... (4n) ... 252
a.0.0.0/5 +7.255.255.255 248.000.000.000 134,217,728 0.0.0.0 7.255.255.255
8A
a = 0 ... (8n) ... 248
a.0.0.0/4 +15.255.255.255 240.000.000.000 268,435,456 0.0.0.0 15.255.255.255 16 A a = 0 ... (16n) ... 240
a.0.0.0/3 +31.255.255.255 224.000.000.000 536,870,912 0.0.0.0 31.255.255.255 32 A a = 0 ... (32n) ... 224
a.0.0.0/2 +63.255.255.255 192.000.000.000 1,073,741,824 0 (64,128,192).0.0.0 63(127,191,255).255.255.255 64 A a = 0, 64, 128, 192
a.0.0.0/1 +127.255.255.255 128.000.000.000 2,147,483,648 0(128).0.0.0 127(255).255.255.255 128 A a = 0, 128
0.0.0.0/0 +255.255.255.255 000.000.000.000 4,294,967,296 0.0.0.0 255.255.255.255 256 A