掩码位、正掩码、反掩码对照表

掩码位	正掩码	反掩码
1	128.0.0.0	127.255.255.255
2	192.0.0.0	63.255.255.255
3	224.0.0.0	31.255.255.255
4	240.0.0.0	15.255.255.255
5	248.0.0.0	7.255.255.255
6	252.0.0.0	3.255.255.255
7	254.0.0.0	1.255.255.255
8	255.0.0.0	0.255.255.255
9	255.128.0.0	0.127.255.255
10	255.192.0.0	0.63.255.255
11	255.224.0.0	0.31.255.255
12	255.240.0.0	0.15.255.255
13	255.248.0.0	0.7.255.255
14	255.252.0.0	0.3.255.255
15	255.254.0.0	0.1.255.255
16	255.255.0.0	0.0.255.255
17	255.255.128.0	0.0.127.255
18	255.255.192.0	0.0.63.255
19	255.255.224.0	0.0.31.255
20	255.255.240.0	0.0.15.255
21	255.255.248.0	0.0.7.255
22	255.255.252.0	0.0.3.255
23	255.255.254.0	0.0.1.255
24	255.255.255.0	0.0.0.255
25	255.255.255.128	0.0.0.127
26	255.255.255.192	0.0.0.63
27	255.255.255.224	0.0.0.31
28	255.255.255.240	0.0.0.15
29	255.255.255.248	0.0.0.7
30	255.255.255.252	0.0.0.3
31	255.255.255.254	0.0.0.1
32	255.255.255.255	0.0.0.0