Number of bits in mask	Netmask	
32	255.255.255.255	
31	255.255.255.254	
30	255.255.255.252	
29	255.255.255.248	
28	255.255.255.240	
27	255.255.255.224	
26	255.255.255.192	
25	255.255.255.128	
24	255.255.255.0	
23	255.255.254.0	
22	255.255.252.0	
21	255.255.248.0	
20	255.255.240.0	
19	255.255.224.0	
18	255.255.192.0	
17	255.255.128.0	
16	255.255.0.0	
15	255.254.0.0	
14	255.252.0.0	
13	255.248.0.0	
12	255.240.0.0	
11	255.224.0.0	
10	255.192.0.0	
9	255.128.0.0	
8	255.0.0.0	
7	254.0.0.0	
6	252.0.0.0	
5	248.0.0.0	
4	240.0.0.0	
3	224.0.0.0	
2	192.0.0.0	
1	128.0.0.0	
0	0.0.0.0