Jan 122014
 

CIDR stands for Classless Inter-Domain Routing. CIDR was developed in the 1990s as a standard scheme for routing network traffic across the Internet.


/27      1/8th of a Class C     32 hosts
/26      1/4th of a Class C     64 hosts
/25      1/2 of a Class C       128 hosts
/24      1 Class C              256 hosts
/23      2 Class C              512 hosts
/22      4 Class C              1,024 hosts
/21      8 Class C              2,048 hosts
/20      16 Class C             4,096 hosts
/19      32 Class C             8,192 hosts
/18      64 Class C             16,384 hosts
/17      128 Class C            32,768 hosts
/16      256 Class C            65,536 hosts (= 1 Class B)
/15      512 Class C            131,072 hosts
/14      1,024 Class C          262,144 hosts
/13      2,048 Class C          524,288 hosts

 
 

CIDR Notation

IPv4 CIDR
IP/CIDR ? to last IP addr Mask Hosts (*) Class Notes
a.b.c.d/32 +0.0.0.0 255.255.255.255 1 1/256 C
a.b.c.d/31 +0.0.0.1 255.255.255.254 2 1/128 C d = 0 … (2n) … 254
a.b.c.d/30 +0.0.0.3 255.255.255.252 4 1/64 C d = 0 … (4n) … 252
a.b.c.d/29 +0.0.0.7 255.255.255.248 8 1/32 C d = 0 … (8n) … 248
a.b.c.d/28 +0.0.0.15 255.255.255.240 16 1/16 C d = 0 … (16n) … 240
a.b.c.d/27 +0.0.0.31 255.255.255.224 32 1/8 C d = 0 … (32n) … 224
a.b.c.d/26 +0.0.0.63 255.255.255.192 64 1/4 C d = 0, 64, 128, 192
a.b.c.d/25 +0.0.0.127 255.255.255.128 128 1/2 C d = 0, 128
a.b.c.0/24 +0.0.0.255 255.255.255.000 256 1 C
a.b.c.0/23 +0.0.1.255 255.255.254.000 512 2 C c = 0 … (2n) … 254
a.b.c.0/22 +0.0.3.255 255.255.252.000 1,024 4 C c = 0 … (4n) … 252
a.b.c.0/21 +0.0.7.255 255.255.248.000 2,048 8 C c = 0 … (8n) … 248
a.b.c.0/20 +0.0.15.255 255.255.240.000 4,096 16 C c = 0 … (16n) … 240
a.b.c.0/19 +0.0.31.255 255.255.224.000 8,192 32 C c = 0 … (32n) … 224
a.b.c.0/18 +0.0.63.255 255.255.192.000 16,384 64 C c = 0, 64, 128, 192
a.b.c.0/17 +0.0.127.255 255.255.128.000 32,768 128 C c = 0, 128
a.b.0.0/16 +0.0.255.255 255.255.000.000 65,536 256 C = 1 B
a.b.0.0/15 +0.1.255.255 255.254.000.000 131,072 2 B b = 0 … (2n) … 254
a.b.0.0/14 +0.3.255.255 255.252.000.000 262,144 4 B b = 0 … (4n) … 252
a.b.0.0/13 +0.7.255.255 255.248.000.000 524,288 8 B b = 0 … (8n) … 248
a.b.0.0/12 +0.15.255.255 255.240.000.000 1,048,576 16 B b = 0 … (16n) … 240
a.b.0.0/11 +0.31.255.255 255.224.000.000 2,097,152 32 B b = 0 … (32n) … 224
a.b.0.0/10 +0.63.255.255 255.192.000.000 4,194,304 64 B b = 0, 64, 128, 192
a.b.0.0/9 +0.127.255.255 255.128.000.000 8,388,608 128 B b = 0, 128
a.0.0.0/8 +0.255.255.255 255.000.000.000 16,777,216 256 B = 1 A
a.0.0.0/7 +1.255.255.255 254.000.000.000 33,554,432 2 A a = 0 … (2n) … 254
a.0.0.0/6 +3.255.255.255 252.000.000.000 67,108,864 4 A a = 0 … (4n) … 252
a.0.0.0/5 +7.255.255.255 248.000.000.000 134,217,728 8 A a = 0 … (8n) … 248
a.0.0.0/4 +15.255.255.255 240.000.000.000 268,435,456 16 A a = 0 … (16n) … 240
a.0.0.0/3 +31.255.255.255 224.000.000.000 536,870,912 32 A a = 0 … (32n) … 224
a.0.0.0/2 +63.255.255.255 192.000.000.000 1,073,741,824 64 A a = 0, 64, 128, 192
a.0.0.0/1 +127.255.255.255 128.000.000.000 2,147,483,648 128 A a = 0, 128
0.0.0.0/0 +255.255.255.255 000.000.000.000 4,294,967,296 256 A

The link below is quite useful for creating CIDR entries:
http://bonomo.info/coyote/cidr-calculator.php

 Posted by at 3:03 pm

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