子网掩码对照表
| 位数 | 掩码 | 可用IP数 |
| 0 | 0.0.0.0 | 4294967294 |
| 1 | 128.0.0.0 | 2147483646 |
| 2 | 192.0.0.0 | 1073741822 |
| 3 | 224.0.0.0 | 536870910 |
| 4 | 240.0.0.0 | 268435454 |
| 5 | 248.0.0.0 | 134217726 |
| 6 | 252.0.0.0 | 67108862 |
| 7 | 254.0.0.0 | 33554430 |
| 8 | 255.0.0.0 | 16777216 |
| 9 | 255.128.0.0 | 8388606 |
| 10 | 255.192.0.0 | 4194302 |
| 11 | 255.224.0.0 | 2097150 |
| 12 | 255.240.0.0 | 1048574 |
| 13 | 255.248.0.0 | 524286 |
| 14 | 255.252.0.0 | 262142 |
| 15 | 255.254.0.0 | 131070 |
| 16 | 255.255.0.0 | 65536 |
| 17 | 255.255.128.0 | 32766 |
| 18 | 255.255.192.0 | 16382 |
| 19 | 255.255.224.0 | 8190 |
| 20 | 255.255.240.0 | 4094 |
| 21 | 255.255.248.0 | 2046 |
| 22 | 255.255.252.0 | 1022 |
| 23 | 255.255.254.0 | 510 |
| 24 | 255.255.255.0 | 254 |
| 25 | 255.255.255.128 | 126 |
| 26 | 255.255.255.192 | 62 |
| 27 | 255.255.255.224 | 30 |
| 28 | 255.255.255.240 | 14 |
| 29 | 255.255.255.248 | 6 |
| 30 | 255.255.255.252 | 2 |
| 31 | 255.255.255.254 | 0 |
| 32 | 255.255.255.255 | 0 |