Valid host address
seanr
Member Posts: 4 ■□□□□□□□□□
in CCNA & CCENT
Can anyone explain a method for fast calculations of valid host addresses within a subnet ?
255.255.224.0 gives us 16 nets with 4094 host per net.
Lets use 172.128.208.0 as the subnet id.
What is the Host Address Range?
Well, I know the first valid host on this subnet is
172.128.208.1
The way I currently calculate this would just to keep adding 255 until I hit 4094. ugh
any shortcuts ?
255.255.224.0 gives us 16 nets with 4094 host per net.
Lets use 172.128.208.0 as the subnet id.
What is the Host Address Range?
Well, I know the first valid host on this subnet is
172.128.208.1
The way I currently calculate this would just to keep adding 255 until I hit 4094. ugh
any shortcuts ?
Comments

dave0212 Member Posts: 287Would that not give you 8 subnets with 8190 hosts??This week I have achieved unprecedented levels of unverifiable productivity
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Learning Python and OSCP 
dtlokee Member Posts: 2,378 ■■■■□□□□□□If you are using a Class B address then:
255.255.224.0 will give you 3 subnet bits and 13 host bits which is 8 subnets and 8190 hosts per subnet. To find the ranges you need to write out all the combinations of subnet bits, then put all "0" or all "1"'s to find the lower and upper bounds respectively.The only easy day was yesterday! 
dave0212 Member Posts: 287I would say the easiest way to calculate quickly is
16 subnets
256/16 is 16 so your increment is 16
Add 16 to the subnet octet and 2 to get your last host
172.128.208.1  172.128.223.254
That is how i do it in my head but i am pretty quick at mental arithmeticThis week I have achieved unprecedented levels of unverifiable productivity
Working on
Learning Python and OSCP 
seanr Member Posts: 4 ■□□□□□□□□□dtlokee wrote:If you are using a Class B address then:
255.255.224.0 will give you 3 subnet bits and 13 host bits which is 8 subnets and 8190 hosts per subnet. To find the ranges you need to write out all the combinations of subnet bits, then put all "0" or all "1"'s to find the lower and upper bounds respectively.
can you give an example of this ? and off topic , can you use a calculator on the exams ? 
laidbackfreak Member Posts: 991seanr wrote:and off topic , can you use a calculator on the exams ?
nope no calculators allowed...... all you get is a wipe board n marker pen....if I say something that can be taken one of two ways and one of them offends, I usually mean the other one :)