Last Updated:
Saturday, 2 November 2013 By: Steve Warner

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Online IPv4 Subnet Mask Calculator

 


 
http://ccna.exampointers.com/sub.php?ip=54.161.192.135&mask=30
http://ccna.exampointers.com/sub.php?ip=92.60.121.54&mask=31
http://ccna.exampointers.com/sub.php?ip=172.16.0.31&mask=30
http://ccna.exampointers.com/sub.php?ip=224.1.0.39&mask=26


/0  0.0.0.0         /1  128.0.0.0       /2  192.0.0.0       /3  224.0.0.0
/4  240.0.0.0       /5  248.0.0.0       /6  252.0.0.0       /7  254.0.0.0

/8  255.0.0.0       /9  255.128.0.0     /10 255.192.0.0     /11 255.224.0.0
/12 255.240.0.0     /13 255.248.0.0     /14 255.252.0.0     /15 255.254.0.0

/16 255.255.0.0     /17 255.255.128.0   /18 255.255.192.0   /19 255.255.224.0
/20 255.255.240.0   /21 255.255.248.0   /22 255.255.252.0   /23 255.255.254.0

/24 255.255.255.0   /25 255.255.255.128 /26 255.255.255.192 /27 255.255.255.224
/28 255.255.255.240 /29 255.255.255.248 /30 255.255.255.252 /31 255.255.255.254

/32 255.255.255.255


My method of working out subnetting for masks that are > /24

If we take the address 192.168.4.18/29

/29 is just the number of bits used for the subnet mask. So the subnet mask will
be 255.255.255.248.

If we use the last octet 248. 256-248 = 8, this means the last octet 0-255 is broken up into 32 groups of 8.


Network Address (18 taken from address above)

integer(18/8) = 2
              * 8
	      = 16
192.168.4.16


Broadcast Address (18 taken from address above)

integer(18/8) = 2
              + 1
	      = 3
	      * 8
	      = 24
	      - 1
	      = 23
192.168.4.23


Inverse Mask

/0  255.255.255.255 /1  127.255.255.255 /2  63.255.255.255  /3  31.255.255.255
/4  15.255.255.255  /5  7.255.255.255   /6  3.255.255.255   /7  1.255.255.255

/8  0.255.255.255   /9  0.127.255.255   /10 0.63.255.255    /11 0.31.255.255
/12 0.15.255.255    /13 0.7.255.255     /14 0.3.255.255     /15 0.1.255.255

/16 0.0.255.255     /17 0.0.127.255     /18 0.0.63.255      /19 0.0.31.255
/20 0.0.15.255      /21 0.0.7.255       /22 0.0.3.255       /23 0.0.1.255

/24 0.0.0.255       /25 0.0.0.127       /26 0.0.0.63        /27 0.0.0.31
/28 0.0.0.15        /29 0.0.0.7         /30 0.0.0.3         /31 0.0.0.1

/32 0.0.0.0

 

 

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