Hi every body!
Let say we have class C 126.96.36.199 network with subnet mask 255.255.255.192
The total number of subnets are:
According to cisco book , the valid subnnets are = total subnets-2
The subnet "188.8.131.52 " and " 184.108.40.206" are not considered valid subnets . My question is why?
Thanks a lot!
To be bit less subtle that Harold, the book you reference is presenting a very old (and out moded) view of the principles of subnetting. In modern practice neither of the subnets is not permitted. (you might however, be careful on certification tests, some of which may still reflect the old practice).
Here's a paper that explains why usage of the subnet zero and all one's subnet was discouraged by RFC950.
Subnet zero and all one's are now widely used.