736 Appendix A: Answers to the "Do I Know This Already?" Quizzes and Q&A Sections
30
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 to 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.
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.
31
Given the IP address 140.1.1.1 and the mask 255.255.255.248, what are all the subnet
numbers if the same (static) mask is used for all subnets in this network?
The Class B network number is 140.1.0.0. The mask implies that the bits 17 to 29, which
are all the bits in the third octet and the first 5 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 table that follows. 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.
Step 2 (only one line shown)
1101 1100 0000 1000 0000 0111
Step 3 (only one line shown)
1101 1100 0000 1000 0000 0111 0000
Step 4
1101 1100 0000 1000 0000 0111 0000 0000
220.8.7.0
Step 5
1101 1100 0000 1000 0000 0111 0001 0000
220.8.7.16
Step 6
1101 1100 0000 1000 0000 0111 0010 0000
220.8.7.32
Step 6
1101 1100 0000 1000 0000 0111 0011 0000
220.8.7.48
Step 6
1101 1100 0000 1000 0000 0111 0100 0000
220.8.7.64
Step 6
1101 1100 0000 1000 0000 0111 0101 0000
220.8.7.80
Skipped a few for brevity
Step 6
1101 1100 0000 1000 0000 0111 1111 0000
220.8.7.240
Step 2 (only one line shown)
1000 1100 0000 0001
Step 3 (only one line shown)
1000 1100 0000 0001 0000 0000 0000 0000
Step 4
1000 1100 0000 0001 0000 0000 0000 1000
140.1.0.0
Step 5
1000 1100 0000 0001 0000 0000 0001 1000
140.1.0.8
Step 6
1000 1100 0000 0001 0000 0000 0010 0000
140.1.0.16
apA.fm Page 736 Monday, March 20, 2000 5:24 PM