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Finding valid subnet masks 1

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corgus

Technical User
Aug 8, 2004
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I am a bit stumped on identifying what subnet masks would be valid for a Class B address wherein you will have 300 subnets with 45 hosts max on each subnet. Looking to see if there is a formula to work out such problems...
 
the way i do it is to start with the /30 subnet, count backwards while doubling the number of host, than subtract 2 when you reach the range your looking for.

for example: 45 host

/30= 4
/29= 8
/28= 16
/27= 32
/26= 64 - 2 = 62 available host


another: 500 host

/30= 4
/29= 8
/28= 16
/27= 32
/26= 64
/25= 128
/24= 256
/23= 512 - 2 = 510 available host

 
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