confused about subnets

saiedsaied Member Posts: 13 ■□□□□□□□□□
i mostly get the subnetting part. however i have some confusions when finiding out subnets.
for example this question was on one of my pre tests and although the videos tell me to use (2^n)-2, the tests indicate that they are using just 2^N. what i dont get is why?

YOu have been assigned an ip address of and have selected as the subnet mask. how may valid subnet addresses are available.

in here they use 2^4 which is 16. shouldnt they use (2^4)-2


  • YFZbluYFZblu Member Posts: 1,462 ■■■■■■■■□□
    The '-2' portion only applies when calculating the number of hosts on a given subnet. The reason you subtract two at the end of host calculation is because the first IP address in a subnet range is the network number, and the last IP address is the broadcast address - Neither of those IP addresses will be assigned to hosts.
  • saiedsaied Member Posts: 13 ■□□□□□□□□□
    ah ok got it. thats what i thought too.

    thanks again bro
  • fadhilfadhil Member Posts: 200
    Before cisco after subnetting, the first and last subnet were not take into consideration thats why they minus 2(2^n -2), some of the books which are not cisco certified use that procedure.but after cisco introduce ip subnet zero all networks take into consideration(can be used).
  • gbdavidxgbdavidx Member Posts: 840
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