Question N318

[b_rasheed]

I believe the question with the subnet 255.255.254.0 is class B
The correct answer is:
186.54.3.0
175.33.4.255
152.35.36.0
26.35.2.255

why 26.35.2.25 is part of the correct answer i did not get it?

Thanks

[black143]

B_Rasheed,

When we do the math on the subnet 255.255.254.0, we find out that we borrow 2 bits in the 3rd octet, and 255 bits in the 4th octet, from the network address.  If you learned how to compute the network address from Cisco, you probably learned about the "magic number", which is simply the "interesting" octet, subtracted from 256.  The magic number is what separates each network subnet from one another.  So, in this case, we use the third octet as the "interesting" octet, do the math, and get a "magic number" of 2 (256-254).  So, this means, each network is separated by 2 in third octet.  For example, if we used the traditional class B network range, we'd get:

172.16.0.0 - 172.16.1.255
172.16.2.0 - 172.16.3.255
172.16.4.0 - 172.16.5.255
172.16.6.0 - 172.16.7.255
172.16.8.0 - 172.16.9.255
etc, etc, etc

Using the question at hand, we can use this math to compute any valid host (excluding the network address and broadcast address).  Your question was specifically regarding 26.35.2.255.  Using my table above, you can see that the answer 26.35.2.255 falls within the second subnet, and isn't a network address (26.35.2.0) or a broadcast address (26.35.3.255) for this subnet. 

Does this make sense?  Anything need clarification?  Good luck with the CCNA!

~ Will