Chapter 7
Reading Organizer
Note: the Reading Organizer has weighted scoring. Any question with the word explain or define in it is
expected to have a longer answer and is worth two points each.
After completion of this chapter, you should be able to:
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Explain the advantages and disadvantages of static routing.
Explain the purpose of different types of static routes.
Configure IPv4 and IPv6 static routes by specifying a next-hop address.
Configure an IPv4 and IPv6 default routes.
Explain the use of legacy classful addressing in network implementation.
Explain the purpose of CIDR in replacing classful addressing.
Design and implement a hierarchical addressing scheme.
Configure an IPv4 and IPv6 summary network address to reduce the number of routing table
updates.
Configure a floating static route to provide a backup connection.
Explain how a router processes packets when a static route is configured.
Troubleshoot common static and default route configuration issues.
7.1 Dynamic Routing Protocols
1. What was one of the first routing protocols used?
Routing Information protocol (RIP)
2. To address the needs of larger networks, two advanced routing protocols were developed. These
are:
a. Open Shortest Path First (OSPF)
b. Intermediate System-to-Intermediate System (IS-IS)
3. Cisco developed two protocols which also scale well in larger network implementations. These are:
a. Interior Gateway Routing Protocol (IGRP)
b. Enhanced IGRP (EIGRP),
4. What protocol was developed to connect different internetworks and provide routing between
them, and connect ISPs and their larger private clients to exchange routing information?
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Border Gateway Protocol (BGP)
5. What are routing protocols are used to facilitate?
The exchange of routing information between routers.
6. The purpose of dynamic routing protocols includes:
a. Discovery of remote networks
b. Maintaining up-to-date routing information
c. Choosing the best path to destination networks
d. Ability to find a new best path if the current path is no longer available
7. List and explain the main components of dynamic routing protocols.
a. Data structures –
Routing protocols typically use tables or databases for its operations. This information is kept in
RAM.
b. Routing protocol messages –
Routing protocols use various types of messages to discover neighboring routers, exchange
routing information, and other tasks to learn and maintain accurate information about the
network.
c. Algorithm –
An algorithm is a finite list of steps used to accomplish a task. Routing protocols use algorithms
for facilitating routing information and for best path determination.
8. What is a primary benefit of dynamic routing protocols?
Routers exchange routing information when there is a topology change.
9. Will a network with moderate levels of complexity have static routing, dynamic routing, or both configured?
Both
10. In the area of data structure, EIGRP creates and maintains what information?
a. Topology Table
b. Neighbor Table
c. Update Table
11. In the area of routing protocol messages, what does EIGRP use?
a. Acknowledgements
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b. Queries
c. Updates
d. Replies
e. Hellos
12. What algorithm does EIGRP use to identify the best route to a network?
DUAL
13. Explain the primary uses static routing has.
a. Providing ease of routing table maintenance in smaller networks that are not expected to
grow significantly.
b. Routing to and from a stub network, which is a network with only one default route out and
no knowledge of any remote networks.
c. Accessing a single default route (which is used to represent a path to any network that does
not have a more specific match with another route in the routing table).
14. What are the disadvantages of using static routing?
a. They are not easy to implement in a large network.
b. Managing the static configurations can become time consuming.
c. If a link fails, a static route cannot reroute traffic.
15. What are the advantages of using dynamic routing protocols?
a. Suitable in all topologies where multiple routers are required.
b. Generally independent of the network size.
c. Automatically adapts topology to reroute traffic if possible.
16. What are the disadvantages of using dynamic routing protocols?
a. Can be more complex to implement.
b. Less secure. Additional configuration settings are required to secure.
c. Route depends on the current topology.
d. Requires additional CPU, RAM, and link bandwidth.
17. Mark the appropriate classification next to each routing type description.
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18. In general, describe the operations of a dynamic routing protocol.
1. The router sends and receives routing messages on its interfaces.
2. The router shares routing messages and routing information with other routers that are
using the same routing protocol.
3. Routers exchange routing information to learn about remote networks.
4. When a router detects a topology change the routing protocol can advertise this change to
other routers.
19. After a router is first booted it learns about any directly connected networks. If a routing protocol
is configured, what is the next step is for the router?
To begin exchanging routing updates to learn about any remote routes.
20. Distance vector routing protocols typically implement a routing loop prevention technique known
as split horizon. Explain.
Split horizon prevents information from being sent out the same interface from which it was
received.
21. What does it mean when a network is converged?
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The network has converged when all routers have complete and accurate information about
the entire network
22. Define convergence time.
Convergence time is the time it takes routers to share information, calculate best paths, and
update their routing tables.
23. Routing protocols can be classified into three different groups according to their characteristics. List
and explain each category.
a. Purpose –
Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)
b. Operation –
Distance vector, link-state protocol, or path-vector protocol
C. Behavior –
Classful (legacy) or classless protocol
24. Based on the curriculum, classify the following IPv4 routing protocols.
a. RIPv2 –
IGP, distance vector, classless protocol
b. EIGRP –
IGP, distance vector, classless protocol developed by Cisco
c. OSPF –
IGP, link-state, classless protocol
d. BGP –
EGP, path-vector, classless protocol
25. What is an autonomous system (AS)?
It is a collection of routers under a common administration such as a company or an
organization.
26. The Internet is based on the AS concept; therefore, two types of routing protocols are required:.
List and explain both.
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a. Interior Gateway Protocols (IGP) –
Used for routing within an AS. It is also referred to as intra-AS routing. Companies,
organizations, and even service providers use an IGP on their internal networks. IGPs include
RIP, EIGRP, OSPF, and IS-IS.
b. Exterior Gateway Protocols (EGP) –
Used for routing between AS. It is also referred to as inter-AS routing. Service providers and
large companies may interconnect using an EGP. The Border Gateway Protocol (BGP) is the only
currently-viable EGP and is the official routing protocol used by the Internet.
27. Define the following terms.
a. Distance –
Identifies how far it is to the destination network and is based on a metric such as the hop
count, cost, bandwidth, delay, and more.
b. Vector –
Specifies the direction of the next-hop router or exit interface to reach the destination.
28. What are four distance vector IPv4 interior gateway protocols?
a. RIPv1
b. RIPv2
c. IGRP
d. EIGRP
29. How is a router configured with a link-state routing protocol different from a router configures with
a distance vector protocol?
The link-state routing protocol can create a complete view or topology of the network by
gathering information from all of the other routers.
30. Explain where Link-state protocols work best.
a. The network design is hierarchical, usually occurring in large networks
b. Fast convergence of the network is crucial
c. The administrators have good knowledge of the implemented link-state routing protocol
31. List two link-state IPv4 IGPs.
a. OSPF
b. IS-IS
32. Explain the biggest distinction between classful and classless routing protocols.
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Classful routing protocols do not send subnet mask information in their routing updates.
Classless routing protocols include subnet mask information in the routing updates.
33. Classful routing protocols create problems in discontiguous networks. Explain what a
discontiguous network is.
A discontiguous network is when subnets from the same classful major network address are
separated by a different classful network address.
34. Classless IPv4 routing protocols all include the subnet mask information with the network address
in routing updates. They also support VLSM and CIDR. List these IPv4 protocols.
a. RIPv2
b. EIGRP
c. OSPF
d. IS-IS
35. Why are all IPv6 routing protocols are considered classless?
Because they include the prefix-length with the IPv6 address.
36. What characteristics can routing protocols can be compared on?
a. Speed of Convergence
b. Scalability
c. Classful or Classless
d. Resource Usage
e. Implementation and Maintenance
37. Based on the curriculum fill in the blanks comparing the routing protocols.
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38. What is the purpose of a routing metric?
To select the best path, the routing protocol must be able to evaluate and differentiate
between the available paths.
7.2 Distance Vector Dynamic Routing
38. How often does RIP send out routing updates?
Every 30 seconds.
39. Identify the routing protocol description that best matches the distance vector routing protocol
description.
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40. What are the key characteristics of RIPv1?
a. Routing updates are broadcasted (255.255.255.255) every 30 seconds.
b. The hop count is used as the metric for path selection.
c. A hop count greater than 15 hops is deemed infinite (too far). That 15th hop router would
not propagate the routing update to the next router.
41. List and explain the improvements introduced in RIPv2.
a. Classless routing protocol –
It supports VLSM and CIDR, because it includes the subnet mask in the routing updates.
b. Increased efficiency –
It forwards updates to multicast address 224.0.0.9, instead of the broadcast address
255.255.255.255.
c. Reduced routing entries –
t supports manual route summarization on any interface.
d. Secure –
It supports an authentication mechanism to secure routing table updates between neighbors.
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42. In 1997, the IPv6 enabled version of RIP was released. RIPng is based on RIPv2. What is Its hop
count and administrative distance?
a. Hop Count 15
b. Administrative distance 120
43. List the design characteristics the Interior Gateway Routing Protocol (IGRP) was developed with.
a. Bandwidth
b. delay
c. load
d. reliability
44. How often are IGRP routing updates broadcast by default?
Every 90 seconds
45. List the differences introduced in EIGRP.
a. Bounded triggered updates
b. Hello keepalive mechanism
c. Maintains a topology table
d. Rapid convergence
e. Multiple network layer protocol support
7.3 RIP and RIPng Routing
46. What command is used to set up RIP on a router?
router rip
47. What command is used to enable RIP routing for the 192.168.1.0 network?
network 192.168.1.0
48. What does the show ip protocols command display?
The IPv4 routing protocol settings currently configured on the router.
49. What does the show ip route command display?
The RIP routes installed in the routing table.
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50. If a router is running RIPv1 and it receives a RIPv2 message, how does it interpret the RIPv2
message.
A RIPv1 router ignores the RIPv2 fields in the route entry.
51. What command is required after the router rip command is issued to force a router to run RIPv2?
version 2
52. What happens on a router running RIPv2 if automatic summarization is disabled?
RIPv2 no longer summarizes networks to their classful address at boundary routers.
53. Sending out unneeded updates on a LAN impacts the network in what ways?
a. Wasted Bandwidth
b. Wasted Resources
c. Security Risk
54. What router configuration command can be used to prevent the transmission of routing updates
through a router interface, but still allow that network to be advertised to other routers?
passive-interface
55. Which routing protocols support the passive-interface command?
All of them
56. To enable an IPv6 router to forward IPv6 packets, what command must be configured?
ipv6 unicast-routing
57. Unlike RIPv2, RIPng is enabled on an interface and not in router configuration mode.
58. The show ipv6 protocols command does not provide the same amount of information as its IPv4
counterpart. What does it confirm?
a. That RIPng routing is configured and running on router R1.
b. The interfaces configured with RIPng.
59. What does the show ipv6 route command display?
The routes installed in the routing table
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7.4 Link-State Dynamic Routing
60. Link-state routing protocols are also known as shortest path first protocols.
61. What are the two IPv4 link-state routing protocols?
a. Open Shortest Path First (OSPF)
b. Intermediate System-to-Intermediate System (IS-IS)
62. The shortest path between two routers is not necessarily the path with the least number of hops.
What does this mean?
The shortest path refers to the path with the lowest cost. Not the smallest number of hops.
63. All routers in a topology will complete the same generic link-state routing process to reach a state
of convergence. Explain each step.
1. Each router learns about its own links and its own directly connected networks. This is done
by detecting that an interface is in the up state.
2. Each router is responsible for meeting its neighbors on directly connected networks. Link
state routers do this by exchanging Hello packets with other link-state routers on directly
connected networks.
3. Each router builds a Link-State Packet (LSP) containing the state of each directly connected
link. This is done by recording all the pertinent information about each neighbor, including
neighbor ID, link type, and bandwidth.
4. Each router floods the LSP to all neighbors. Those neighbors store all LSPs received in a
database. They then flood the LSPs to their neighbors until all routers in the area have received
the LSPs. Each router stores a copy of each LSP received from its neighbors in a local database.
5. Each router uses the database to construct a complete map of the topology and computes
the best path to each destination network. Like having a road map, the router now has a
complete map of all destinations in the topology and the routes to reach them. The SPF
algorithm is used to construct the map of the topology and to determine the best path to each
network.
64. Routers with link-state routing protocols use a Hello protocol to discover any neighbors on its links.
What is a neighbor?
A neighbor is any other router that is enabled with the same link-state routing protocol.
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65. What happens if a router stops receiving Hello packets from a neighbor?
That neighbor is considered unreachable and the adjacency is broken.
66. LSPs do not need to be sent periodically. When do LSPs needs to be sent?
a. During initial startup of the routing protocol process on that router (e.g., router restart)
b. Whenever there is a change in the topology
67. List the advantages of link-state routing protocols compared to distance vector routing protocols.
a. Builds a Topological Map
b. Fast Convergence
c. Event-driven
d. Hierarchical Design
68. List the disadvantages link-state protocols have compared to distance vector routing protocols?
a. Memory Requirements
b. Processing Requirements
c. Bandwidth Requirements
69. Modern link-state routing protocols are designed to minimize the effects on:
a. memory
b. CPU
c. bandwidth
7.5 The Routing Table
70. What information do automatically configured routing table entries contain?
a. Route source
b. Destination network
c. Outgoing interface
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71. Explain what each of the following routing table codes indicate.
S - Identifies that the route was manually created by an administrator to reach a specific
network. This is known as a static route.
D - Identifies that the route was learned dynamically from another router using the EIGRP
routing protocol.
O - Identifies that the route was learned dynamically from another router using the OSPF
routing protocol.
R - Identifies that the route was learned dynamically from another router using the RIP routing
protocol.
72. Define the following terms:
a. Route source –
Identifies how the route was learned.
b. Destination network –
Identifies the address of the remote network.
c. Administrative distance –
Identifies the trustworthiness of the route source.
d. Metric –
Identifies the value assigned to reach the remote network. Lower values indicate preferred
routes.
e. Next hop –
Identifies the IPv4 address of the next router to forward the packet to.
f. Route timestamp –
Identifies from when the route was last heard.
g. Outgoing interface –
Identifies the exit interface to use to forward a packet toward the final destination.
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73. Identify the sections of the routing table entry.
74. What is an ultimate route?
I
is a routing table entry that contains either a next-hop IPv4 address or an exit interface.
75. What are three examples of ultimate routes?
a. Directly connected
b. dynamically learned
c. local routes
76. A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network
address. List and explain three types of level 1 routes.
a. Network route –
A network route that has a subnet mask equal to that of the classful mask.
b. Supernet route –
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A supernet route is a network address with a mask less than the classful mask, for example, a
summary address.
c. Default route –
A default route is a static route with the address 0.0.0.0/0.
77. The source of the level 1 route can be a:
a. directly connected network
b. static route
c. a dynamic routing protocol
78. A level 1 parent route is a level 1 network route that is subnetted. A parent route can never be an
ultimate route.
79. A level 2 child route is a route that is a subnet of a classful network address.
80. Using the routing table locate the networks listed in the chart. Determine whether the networks
are classified as Level 1, Level 1 Parent, or Level 2 Child routes.
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81. The best match is the route in the routing table that has the most number of far left matching bits
with the destination IPv4 address of the packet. What is the route with the greatest number of
equivalent far left bits, or the longest match?
It is always the preferred route.
82. IPv6 is classless by design, all routes are effectively level 1 ultimate routes. There is no level 1
parent of level 2 child routes.
83. List and explain what information directly connected route entries display in a show IPv6 routing
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Route source - Identifies how the route was learned. Directly connected interfaces have two
route source codes (C identifies a directly connected network while L identifies that this is a
local route.)
a. Directly connected network –
The IPv6 address of the directly connected network.
b. Administrative distance –
Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. A value
of 0 indicates the best, most trustworthy source.
c. Metric –
Identifies the value assigned to reach the remote network. Lower values indicate preferred
routes.
d. Outgoing interface –
Identifies the exit interface to use when forwarding packets to the destination network.
84. Label the parts of an IPv6 routing table entry.
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