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Chapter 3

IP Addressing

Answers to Review Questions

C. A leading bit pattern of 0 indicates a Class A network. A leading bit
pattern of 10 indicates a Class B network. A leading bit pattern of 110
indicates a Class C network.

D. Network 127 is reserved for loopback purposes (e.g., for trouble-
shooting diagnostics). With a local loopback address, a host can send
a test packet to itself without generating network traffic.

B, C. The formula 2

2 = number of hosts (where n is the number of

host bits in the subnet mask) tells us how many hosts can be supported
for a particular subnet. Here are some examples:

255.255.255.240 => 4 host bits => 14 hosts

255.255.255.0 => 8 host bits => 254 hosts

255.255.255.192 => 6 host bits => 62 hosts

255.255.255.224 => 5 host bits => 30 hosts

B, D. VLSM is compatible only with classless routing protocols.
Classless routing protocols have the ability to carry subnet informa-
tion in their route advertisements. RIPv1 and IGRP are classful,
whereas RIPv2 and EIGRP are classless.

A. Route summarization, which works best with contiguous address
space, reduces the memory and processor burden on routers by repre-
senting multiple subnets in a single route advertisement.

D. If you write out the networks 172.16.100.0/24 and 172.16.106.0/
24 in binary and see how many leading bits they have in common, you
will find that the first 20 bits are the same for both networks. If you
then convert these 20 bits back into decimal, you will have the address
of the summarized route.

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