Chapter 9
Reading Organizer
After completion of this chapter, you should be able to:
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Explain why routing is necessary for hosts on different networks to communicate.
Describe IP as a communication protocol used to identify a single device on a network.
Given a network and a subnet mask, calculate the number of host addresses available.
Calculate the necessary subnet mask in order to accommodate the requirements of a network.
Describe the benefits of variable length subnet masking (VLSM)
Explain how IPv6 address assignments are implemented in a business network.
9.1 Subnetting an IPv4 Network
1. Explain how flat network design operates.
All devices in an organization are assigned an IP address with a matching network ID.
2. Define subnetting.
The process of segmenting a network, by dividing it into multiple smaller network spaces.
3. What device is required to forward traffic between different networks?
Router
4. The address plan includes:
a. deciding the needs for each subnet in terms of size
b. how many hosts per subnet
c. how host addresses will be assigned
d. which hosts will require static IP addresses
e. which hosts can use DHCP for obtaining their addressing information
5. What are the three private IP addresses ranges?
a. 10.0.0.0 with a subnet mask of 255.0.0.0
b. 172.16.0.0 with a subnet mask of 255.240.0.0
c. 192.168.0.0 with a subnet mask of 255.255.0.0
6. Who typically allocates public IP addresses?
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Robb Jones
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Public addresses used to connect to the Internet are typically allocated from a service provider.
7. Two very important factors that will lead to the determination of which private address block is
required, are:
a. the number of subnets required
b. the maximum number of hosts needed per subnet
8. Where is the only place you can borrow bits from?
Bits can only be borrowed from the host portion of the address.
9. Explain the guidelines for subnets:
a. Network address –
All 0 bits in the host portion of the address.
b. First host address –
All 0 bits plus a right-most 1 bit in the host portion of the address.
c. Last host address –
All 1 bits plus a right-most 0 bit in the host portion of the address.
D. Broadcast address –
All 1 bits in the host portion of the address.
10. What command would you use to give a Gigabit interface the IP address and subnet mask
192.168.1.1 255.255.255.0?
R1(config)#interface gigabitethernet 0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
11. What is the formula for calculating the number of subnets?
2^n (where n = the number of bits borrowed)
12. Enter the correct network address in binary and decimal format.
2
13. How many usable hosts are available with this network?
14. Define the range of hosts, the broadcast address and the next network address in decimal format.
Cisco Semester 1 – Introduction to Networks 5.0
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Robb Jones
Chapter 9
Frederick County Career & Tech Center, MD
15. Enter the binary representation of the subnet mask in the octet fields provided.
16. Enter the network address in binary and decimal format in the octet fields.
17. Enter the number of usable hosts.
4
18. Define the range of hosts, the broadcast address, and the next network address.
19. There are two considerations when planning subnets. These are:
a. the number of host addresses required for each network
b. the number of individual subnets needed
20. What is the key to determine the number of subnets and hosts needed in a network?
The key is to balance the number of subnets needed and the number of hosts required for the
largest subnet.
21. How many addresses are needed for point-to-point WAN links?
Two hosts
Cisco Semester 1 – Introduction to Networks 5.0
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Robb Jones
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Frederick County Career & Tech Center, MD
22. What was subnetting a subnet, or using Variable Length Subnet Mask (VLSM), was designed to
avoid?
Wasting addresses.
23. Traditional subnetting creates subnets of equal size. Each subnet in a traditional scheme uses the
same subnet mask. What does VLSM allow?
VLSM allows a network space to be divided in unequal parts
24. When the number of needed host addresses is known, what formula is used to determine the
hosts?
2^n-2
9.2 Addressing Schemes
25. There are three primary considerations when planning address allocation. List and explain each.
a. Preventing Duplication of Addresses –
Each host in an internetwork must have a unique address. Without the proper planning and
documentation, an address could be assigned to more than one host, resulting in access issues for both
hosts.
b. Providing and Controlling Access –
Some hosts, such as servers, provide resources to internal hosts as well as to external hosts. The Layer 3
address assigned to a server can be used to control access to that server. If, however, the address is
randomly assigned and not well documented, controlling access is more difficult.
c. Monitoring Security and Performance –
Similarly, the security and performance of network hosts and the network as a whole must be
monitored. As part of the monitoring process, network traffic is examined for addresses that are
generating or receiving excessive packets. If there is proper planning and documentation of the
network addressing, problematic network devices can be easily found.
26. Within a network, there are different types of devices, including:
a. End user clients
b. Servers and peripherals
c. Hosts that are accessible from the Internet
d. Intermediary devices
e. Gateway
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9.3 Design Considerations for IPv6
27. An IPv6 address space is not subnetted to conserve addresses. Why is it subnetted?
It is subnetted to support hierarchical, logical design of the network.
28. An IPv6 address block with a /48 prefix has 16 bits for subnet ID. How many addresses are available
using the 16 bit subnet ID?
65,536 /64 subnets
How many bits are borrowed from the interface ID in this scenario?
None
29. How many addresses are available in each IPv6 /64 subnet?
Roughly eighteen quintillion addresses
30. In IPv4 you can borrow bits from the host portion of an address Where can you borrow bits from in
IPv6 to create additional IPv6 subnets?
The interface ID
31. Explain why are bit borrowed in IPv6?
This is typically done for security reasons to create fewer hosts per subnet and not necessarily
to create additional subnets.
32. When extending the subnet ID by borrowing bits from the interface ID, the best practice is to
subnet on a ___nibble boundary___.
33. What is a nibble?
It is 4 bits or one hexadecimal digit.
Cisco Semester 1 – Introduction to Networks 5.0
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Robb Jones
Chapter 9
Frederick County Career & Tech Center, MD
34. Subnetting on nibble boundaries means only using nibble aligned subnet masks. Starting at /64, the
nibble aligned subnet masks are:
a. /68
b. /72
c. /76
d. /80
e. /84
f. /88
g. /92
35. It is possible to subnet within a nibble boundary, within a hexadecimal digit, but it is not
recommended or even necessary. Explain why.
Subnetting within a nibble takes away the advantage easily determining the prefix from the
interface ID.
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