Subnetting Question confusion

Humper

I can do the subnetting questions out of Todd Lamles CCNA self-study guide fine...But I went to the subnettingquestions.com website and got this question.


Question: What is the first valid host on the subnetwork that the node 172.28.254.135 255.255.252.0 belongs to?

Answer: 172.28.252.1

I realize its a /22 with 6 subnet bits and 10host bits -- theres 64 subnets and 1024 hosts per subnet? Is that right? or is it total hosts?

I get confused by this question because I guess I can't go backwards. How do I find the first valid host from the information given to me in this question? I think I am missing something really simple, any help would be appreciated! Thanks

gojericho0

Question: What is the first valid host on the subnetwork that the node 172.28.254.135 255.255.252.0 belongs to?

Answer: 172.28.252.1

I realize its a /22 with 6 subnet bits and 10host bits -- theres 64 subnets and 1024 hosts per subnet? Is that right? or is it total hosts?

172.28.254.135 /22 is a host in the range of the subnet:

172.28.252.0 - 172.28.255.255

So you can see there is 1024 hosts per subnet and the original class be address is originally being broken down into 64 sections.

The first section would be:

172.28.0.0 - 172.28.3.255 with the first host being 172.28.0.1

Does this make more sense?[/quote]

EricO

You should really do the logical anding of the subnet mask and the network address to find the answer.


11111111.11111111.11111100.00000000
x
10101100.00011100.11111111.10000111

=
10101100.00011100.11111100.00000000
or

172.28.252.0

and of course eliminating the zero would give the the first available host of

172.28.252.1