Ccna routing and Switching Complete Study Guide

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Determine possible block sizes.    This is an important part of understanding IP address-

ing and subnetting. The valid block sizes are always 2, 4, 8, 16, 32, 64, 128, etc. You can 

determine your block size by using the 256-subnet mask math.

Describe the role of a subnet mask in IP addressing.    A subnet mask is a 32-bit value that 

allows the recipient of IP packets to distinguish the network ID portion of the IP address 

from the host ID portion of the IP address.

Understand and apply the 2

x

 – 2 formula.    Use this formula to determine the proper sub-

net mask for a particular size network given the application of that subnet mask to a par-

ticular classful network.

Explain the impact of Classless Inter-Domain Routing (CIDR).    CIDR allows the creation 

of networks of a size other than those allowed with the classful subnetting by allowing 

more than the three classful subnet masks.

Written Labs

In this section, you’ll complete the following labs to make sure you’ve got the information 

and concepts contained within them fully dialed in:

Lab 4.1: Written Subnet Practice #1

Lab 4.2: Written Subnet Practice #2

Lab 4.3: Written Subnet Practice #3

You can find the answers to these labs in Appendix A, “Answers to Written Labs.”