CCENT/CCNA ICND1 100-101 Official Cert Guide

Chapter 19

1. A. With 50 percent growth, the mask needs to define enough subnet bits to create 150 subnets. As a result, the mask needs at least 8 subnet bits (7 subnet bits supply 2⁷, or 128, subnets, and 8 subnet bits supply 2⁸, or 256, subnets). Similarly, the need for 50 percent growth in the size for the largest subnet means that the host part needs enough bits to number 750 hosts/subnet. Nine host bits are not enough (2⁹ – 2 = 510), but 10 host bits supply 1022 hosts/subnet (2¹⁰ – 2 = 1022). With 16 network bits existing because of the choice to use a Class B network, the design needs a total of 34 bits (at least) in the mask (16 network, 8 subnet, 10 host), but only 32 bits exist—so no single mask meets the requirements.

2. B. With a ...