# iptab
+----------------------------------------------+
| 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  255.255.255.0   |
|   512      9    /23      2C  255.255.254.0   |
|    1K     10    /22      4C  255.255.252.0   |
|    2K     11    /21      8C  255.255.248.0   |
|    4K     12    /20     16C  255.255.240.0   |
|    8K     13    /19     32C  255.255.224.0   |
|   16K     14    /18     64C  255.255.192.0   |
|   32K     15    /17    128C  255.255.128.0   |
|   64K     16    /16      1B  255.255.0.0     |
|  128K     17    /15      2B  255.254.0.0     |
|  256K     18    /14      4B  255.252.0.0     |
|  512K     19    /13      8B  255.248.0.0     |
|    1M     20    /12     16B  255.240.0.0     |
|    2M     21    /11     32B  255.224.0.0     |
|    4M     22    /10     64B  255.192.0.0     |
|    8M     23     /9    128B  255.128.0.0     |
|   16M     24     /8      1A  255.0.0.0       |
|   32M     25     /7      2A  254.0.0.0       |
|   64M     26     /6      4A  252.0.0.0       |
|  128M     27     /5      8A  248.0.0.0       |
|  256M     28     /4     16A  240.0.0.0       |
|  512M     29     /3     32A  224.0.0.0       |
| 1024M     30     /2     64A  192.0.0.0       |
| 2048M     31     /1    128A  128.0.0.0       |
| 4096M     32     /0    256A  0.0.0.0         |
+----------------------------------------------+
			

$ sudo apt-get install netmask
			

-s, --standard Output address/netmask pairs

$ netmask -s 192.168.1.0/28
    192.168.1.0/255.255.255.240

$ netmask -s 192.168.1.0/24
    192.168.1.0/255.255.255.0  

$ netmask -s 192.168.1.0/24
    192.168.1.0/255.255.255.0  

$ netmask -s 192.168.1.0/26
    192.168.1.0/255.255.255.192
			

-c, --cidr Output CIDR format address lists

$ netmask -c 192.168.1.0/255.255.255.252
    192.168.1.0/30

$ netmask -c 192.168.1.0/255.255.255.192
    192.168.1.0/26

$ netmask -c 192.168.1.0/255.255.255.240
    192.168.1.0/28
			

-i, --cisco Output Cisco style address lists 思科風格的反子網掩碼計算

$ netmask  -i 192.168.1.0/255.255.255.0
    192.168.1.0 0.0.0.255      

$ netmask  -i 192.168.1.0/255.255.255.252
    192.168.1.0 0.0.0.3        

$ netmask  -i 192.168.1.0/24
    192.168.1.0 0.0.0.255      

$ netmask  -i 192.168.1.0/28
    192.168.1.0 0.0.0.15  
			

-r, --range Output ip address ranges 輸出地址範圍

$ netmask  -r 192.168.1.0/255.255.255.0
    192.168.1.0-192.168.1.255   (256)

$ netmask  -r 192.168.1.0/255.255.255.192
    192.168.1.0-192.168.1.63    (64)
    
$ netmask  -r 192.168.1.0/255.255.255.252
    192.168.1.0-192.168.1.3     (4)
    
$ netmask  -r 192.168.1.0/28
    192.168.1.0-192.168.1.15    (16)
    
$ netmask  -r 192.168.1.0/24
    192.168.1.0-192.168.1.255   (256)
			

$ netmask -r 192.168.1.0/255.255.255.252
    192.168.1.0-192.168.1.3     (4)

$ netmask -r 192.168.1.2/255.255.255.252
    192.168.1.0-192.168.1.3     (4)

$ netmask -r 192.168.1.6/255.255.255.252
    192.168.1.4-192.168.1.7     (4)

$ netmask -r 192.168.1.12/255.255.255.252
   192.168.1.12-192.168.1.15    (4)

$ netmask -r 192.168.1.13/255.255.255.252
   192.168.1.12-192.168.1.15    (4)

$ netmask -r 192.168.1.100/255.255.255.252
  192.168.1.100-192.168.1.103   (4)

$ netmask -r 192.168.1.100/255.255.255.240
   192.168.1.96-192.168.1.111   (16)

$ netmask -r 192.168.1.50/255.255.255.240
   192.168.1.48-192.168.1.63    (16)			
			

-b, --binary Output address/netmask pairs in binary 二進制

$ netmask -b 192.168.1.0/255.255.255.240
11000000 10101000 00000001 00000000 / 11111111 11111111 11111111 11110000

$ netmask -b 172.16.0.0/255.255.252.0
10101100 00010000 00000000 00000000 / 11111111 11111111 11111100 00000000