Wednesday, June 22, 2016

How to cut a network in half

/* This fluff headed manager would like to thank Judy Novak, Andrew Laman and David Hoelzer for their help in creating this blog post */

In a course that I will be teaching in Boston, Management 512, Security Leadership Essentials for Managers, there is a lab that asks how to cut a network in half.
NOTE: If you are a current or prospective MGT 512 student, do not panic. You are not expected to know the fine points below. The context of the lab is that you are conducting a job interview and the candidate is a network engineer that is expected to know this material.

Original network:

  • Public or private? Private
  • Network and broadcast addresses:, broadcast
  • Range of valid host addresses: -  with exceptions: 
The .0 address is the network address and is not a usable host address.  When we change the subnet mask to or /25, the two "network" addresses for the same range become and  The broadcast addresses become and  There are now four addresses that are not usable: .0, .127, .128, .255.

Cut the network in half. = network address 1 = broadcast address 1 to valid host addresses = network address 2 = broadcast address 2 to valid host addresses

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