726 Appendix A: Answers to the "Do I Know This Already?" Quizzes and Q&A Sections
7
Given the IP address 200.1.1.130 and the mask 255.255.255.224, what are the assignable
IP addresses in this subnet?
The subnet number is 200.1.1.128, and the subnet broadcast address is 200.1.1.159. The
assignable addresses are all the addresses between the subnet and broadcast addresses,
namely 200.1.1.129 to 200.1.1.158.
8
Given the IP address 220.8.7.100 and the mask 255.255.255.240, what are all the subnet
numbers if the same (static) mask is used for all subnets in this network?
The Class C network number is 220.8.7.0. The mask implies that the bits 25 through 28,
which are the first 4 bits in the fourth octet, comprise the subnet field. Essentially, the
subnet numbers have the same numbers in the network portion and the same (all binary 0)
value in the host portion of the number. Each individual subnet number has a unique value
in the subnet portion of the number.
The binary algorithm is shown in the following table. Refer to the section "Given a
Network Number and a Static Subnet Mask, What Are the Valid Subnet Numbers?" in
Chapter 5 for a review of the algorithm.
9
Create a minimal configuration enabling IP on each interface on a 2501 router (two
serial, one Ethernet). The NIC assigned you network 8.0.0.0. Your boss says that you need,
at most, 200 hosts per subnet. You decide against using VLSM. Your boss says to plan your
subnets so that you can have as many subnets as possible, rather than allow for larger
First three octets in binary
1101 1100 0000 1000 0000 0111
Host field with all zeros added
1101 1100 0000 1000 0000 0111 0000
All binary 0 subnet field added,
completing the first subnet
number
1101 1100 0000 1000 0000 0111 0000 0000
220.8.7.0
Added binary 1 to subnet field,
giving second subnet number
1101 1100 0000 1000 0000 0111 0001 0000
220.8.7.16
Added binary 1 to subnet field,
giving third subnet number
1101 1100 0000 1000 0000 0111 0010 0000
220.8.7.32
Added binary 1 to subnet field,
giving fourth subnet number
1101 1100 0000 1000 0000 0111 0011 0000
220.8.7.48
Added binary 1 to subnet field,
giving fifth subnet number
1101 1100 0000 1000 0000 0111 0100 0000
220.8.7.64
Added binary 1 to subnet field,
giving sixth subnet number
1101 1100 0000 1000 0000 0111 0101 0000
220.8.7.80
Skipped a few for brevity
Last subnet number
1101 1100 0000 1000 0000 0111 1111 0000
220.8.7.240
apA.fm Page 726 Monday, March 20, 2000 5:24 PM