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network-programmingcomputer-scienceaddressing

Classless addressing

Your router has the IP address of 216.83.11.65/27. You wish to connect a new system on the network. Which of the following addresses would you assign to the new system.

  • A: 216.83.11.45
  • B: 216.83.11.87
  • C: 216.83.11.95
  • D: 216.83.11.96

The answer is B, but I'm not sure why. Can I get a step by step breakdown?

Solution

  • Your host network can chose from all the bits in the IP address, that are not used to define the network.1

    So when looking at the Network Configuration you have, your network has the following range (you can use a subnet calculator to get to these values):

    216.83.11.65 - 216.83.11.94

    This rules out A and D, because you will need a router to get there (since the IP addresses cannot be directly reached within the network).

    Your network internal broadcast address will be 216.83.11.95. This rules out answer C, because a host cannot have the broadcast address of your network.

    So, only answer B stands.

    1 I know that this might not be understandable at all. Cannot do it better. In this case please refer to Wikipedia: Classless Inter-Domain Routing