+----------------------------------------------+
                  |addrs   bits   pref   class   mask            |
                  +----------------------------------------------+
                  |    1      0    /32           255.255.255.255 |
                  |    2      1    /31           255.255.255.254 |
                  |    4      2    /30           255.255.255.252 |
                  |    8      3    /29           255.255.255.248 |
                  |   16      4    /28           255.255.255.240 |
                  |   32      5    /27           255.255.255.224 |
                  |   64      6    /26           255.255.255.192 |
                  |  128      7    /25           255.255.255.128 |
                  |  256      8    /24      1C   255.255.255     |
                  |  512      9    /23      2C   255.255.254     |
                  |   1K     10    /22      4C   255.255.252     |
                  |   2K     11    /21      8C   255.255.248     |
                  |   4K     12    /20     16C   255.255.240     |
                  |   8K     13    /19     32C   255.255.224     |
                  |  16K     14    /18     64C   255.255.192     |
                  |  32K     15    /17    128C   255.255.128     |
                  |  64K     16    /16      1B   255.255         |
                  | 128K     17    /15      2B   255.254         |
                  | 256K     18    /14      4B   255.252         |
                  | 512K     19    /13      8B   255.248         |
                  |   1M     20    /12     16B   255.240         |
                  |   2M     21    /11     32B   255.224         |
                  |   4M     22    /10     64B   255.192         |
                  |   8M     23     /9    128B   255.128         |
                  |  16M     24     /8      1A   255             |
                  |  32M     25     /7      2A   254             |
                  |  64M     26     /6      4A   252             |
                  | 128M     27     /5      8A   248             |
                  | 256M     28     /4     16A   240             |
                  | 512M     29     /3     32A   224             |
                  |1024M     30     /2     64A   192             |
                  +----------------------------------------------+

                   10.0.0.0    - 10.255.255.255  (10/8 )
                   172.16.0.0  - 172.31.255.255  (172.16/12 )
                   192.168.0.0 - 192.168.255.255 (192.168/16 )

-------------------------------------------------------------------------------

Пример разбивки сети классы С на подсети с указанием сети и B'cast 
+---------------+---------+----+---------+-------+------+-------+-------------+
| Сетевая маска | Подсети |Сеть|  B'cast | MinIP | MaxIP| Хосты | Всего хостов|
+---------------+---------+----+---------+-------+------+-------+-------------+
      128            2       0     127       1     126    126
                           128     255     129     254    126     252

      192            4       0      63       1      62     62
                            64     127      65     126     62
                           128     191     129     190     62
                           192     255     193     254     62     248

      224            8       0      31       1      30     30
                            32      63      33      62     30
                            64      95      65      94     30
                            96     127      97     126     30
                           128     159     129     158     30
                           160     191     161     190     30
                           192     223     193     222     30
                           224     255     225     254     30     240
-------------------------------------------------------------------------------