CIDR Conversion Table

CIDR Length	Mask	# Networks	# Hosts
/1	128.0.0.0	128 A	2,147,483,392
/2	192.0.0.0	64 A	1,073,741,696
/3	224.0.0.0	32 A	536,870,848
/4	240.0.0.0	16 A	268,435,424
/5	248.0.0.0	8 A	134,217,712
/6	252.0.0.0	4 A	67,108,856
/7	254.0.0.0	2 A	33,554,428
/8	255.0.0.0	1 A	16,777,214
/9	255.128.0.0	128 B	8,388,352
/10	255.192.0.0	64 B	4,194,176
/11	255.224.0.0	32 B	2,097,088
/12	255.240.0.0	16 B	1,048,544
/13	255.248.0.0	8 B	524,272
/14	255.252.0.0	4 B	262,136
/15	255.254.0.0	2 B	131,068
/16	255.255.0.0	1 B	65,024
/17	255.255.128.0	128 C	32,512
/18	255.255.192.0	64 C	16,256
/19	255.255.224.0	32 C	8,128
/20	255.255.240.0	16 C	4,064
/21	255.255.248.0	8 C	2,032
/22	255.255.252.0	4 C	1,016
/23	255.255.254.0	2 C	508
/24	255.255.255.0	1 C	254
/25	255.255.255.128	2 subnets	124
/26	255.255.255.192	4 subnets	62
/27	255.255.255.224	8 subnets	30
/28	255.255.255.240	16 subnets	14
/29	255.255.255.248	32 subnets	6
/30	255.255.255.252	64 subnets	2
/31	255.255.255.254	none	none
/32	255.255.255.255	1/256 C	1

 

A network is called a supernet when the prefix boundary contains fewer bits than the network's natural (i.e. classful) mask. A network is called a subnet when the prefix boundary contains more bits than the network's natural mask.

Examples
209.60.128.0 is a class C network address with a natural mask of /24.
209.60.128.0 /22 is a supernet which yields:
209.60.128.0 /24
209.60.129.0 /24
209.60.130.0 /24
209.60.131.0 /24

192.0.0.0 /25
Subnet    Host Range
  0        192.0.0.1      -  192.0.0.126
  1        192.0.0.129  -  192.0.0.254

192.0.0.0 /26
Subnet Host Range
0 192.0.0.1 - 192.0.0.62
1 192.0.0.65 - 192.0.0.126
2 192.0.0.129 - 192.0.0.190
3 192.0.0.193 - 192.0.0.254

192.0.0.0 /27
Subnet Host Range
0 192.0.0.1 - 192.0.0.30
1 192.0.0.33 - 192.0.0.62
2 192.0.0.65 - 192.0.0.94
3 192.0.0.97 - 192.0.0.126
4 192.0.0.129 - 192.0.0.158
5 192.0.0.161 - 192.0.0.190
6 192.0.0.193 - 192.0.0.222
7 192.0.0.225 - 192.0.0.254

  

Reserved Network Numbers

Class	Start	End	# Hosts	Comment
A	10.0.0.0	10.255.255.255	16,777,216	a single Class A network number
B	172.16.0.0	172.31.255.255	1,048,544	16 contiguous Class B network numbers
C	192.168.0.0	192.168.255.255	65,534	256 contiguous Class C network numbers