Prefix 
length	Subnet mask	#Hosts	Start	Pre-allocated
/1	128.0.0.0 		
/2	192.0.0.0 		
/3	224.0.0.0 	
/4	240.0.0.0 	
/5	248.0.0.0 	
/6	252.0.0.0 	
/7	254.0.0.0 	
/8	255.0.0.0 	
/9	255.128.0.0 	
/10	255.192.0.0 	
/11	255.224.0.0 	
/12	255.240.0.0 	
/13	255.248.0.0 	
/14	255.252.0.0 	
/15	255.254.0.0 	
/16	255.255.0.0	65536
/17	255.255.128.0 	32768
/18	255.255.192.0 	16384
/19	255.255.224.0 	8192
/20	255.255.240.0 	4096
/21	255.255.248.0 	2048
/22	255.255.252.0 	1024
/23	255.255.254.0 	512     
/24	255.255.255.0 	256	0
/25	255.255.255.128 128	0	0-7,127
/25     255.255.255.128 128	128	128-135,255
/26	255.255.255.192	64	0	0-7,63
/26	255.255.255.192	64	64	64-71,127
/26	255.255.255.192	64	128	128-135,191
/26	255.255.255.192	64	192	192-199.255
/27	255.255.255.224 32
/28	255.255.255.240 16
/29	255.255.255.248 8
/30	255.255.255.252 4
/31	255.255.255.254 2
/32	255.255.255.255	1