CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 7-1
Chapter 7
Routing Protocols
At a Glance
Instructor’s Manual Table of Contents
• Overview
• Objectives
• Teaching Tips
• Quick Quizzes
• Class Discussion Topics
• Additional Projects
• Additional Resources
• Key Terms
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 7-2
Lecture Notes
Overview
This chapter explains the concepts of nonroutable, routed, and routing protocols, with a
discussion of major protocols in each category. The chapter also examines the distinction
between distance-vector and link-state routing protocols. In addition, you will learn the
proper way to configure and monitor the Routing Information Protocol (RIPv1) on Cisco
routers. This chapter also presents the concepts and techniques required to configure static
routing and default routes.
Chapter Objectives
• Differentiate between nonroutable, routed, and routing protocols
• Define Interior Gateway Protocols, Exterior Gateway Protocols, distance-vector routing
protocols, and link-state routing protocols
• Explain the concepts of count-to-infinity, split horizon, split horizon with poison
reverse, and hold-down timers
• Describe, configure, and monitor the interior routing protocol RIP
• Explain static routing and administrative distance
• Configure static routing and default routes
Teaching Tips
Nonroutable Protocols
1. Explain that in the early days of networking, networks were small collections of
2. Explain that early networks were sometimes configured as peer-to-peer networks, in
4. Define NetBEUI (NetBIOS Enhanced User Interface) as the most common nonroutable
protocol. It ships with all Microsoft Windows operating systems. NetBEUI cannot scale
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 7-3
Teaching
Tip
If you try to use NetBEUI—or any nonroutable protocol—in a network with
multiple networks, communication between the networks will fail.
Routed Protocols
1. Explain that routed protocols have packet headers that can contain Network layer
2. Mention that protocols that can carry Network layer information include:
3. Explain that for routed protocols to work on a network, every device must be
configured with a unique IP or IPX address (logical address). Use Figure 7-3 to
illustrate your explanation.
Teaching
Tip
IPX/SPX is a proprietary protocol suite developed by Novell. While it is
routable, it cannot be routed across the Internet like TCP/IP and therefore is
limited.
Routing Protocols
1. Define routing protocols as protocols used by routers to make path determination
2. Define hop count as the number of routers a packet must pass through to reach a
3. Define autonomous system (AS) as a group of routers under the control of a single
administration. An AS uses Interior Gateway Protocols as routing protocols. Use Figure
4. Define Interior Gateway Protocols (IGPs) as routing protocols used within an AS.
5. Examples of IGPs include:
a. Routing Information Protocol (RIP)
6. Border Gateway Protocol (BGP) is an example of EGP.
Teaching
Tip
Read more about autonomous systems (AS) at:
http://en.wikipedia.org/wiki/Autonomous_system_(Internet).
Two Types of IGPs
1. Explain that distance-vector routing protocols broadcast their entire routing table to
each neighbor router at predetermined intervals. The actual interval depends on the
2. Explain that distance-vector routing protocols suffer from slow time to convergence.
3. Mention that one of the problems with distance-vector routing protocols is routing
7-7 to illustrate your explanation.
4. Explain that defining a maximum is one of the easiest ways to limit count–to-infinity
problems. Split horizon and split horizon with poison reverse are two other common
Split horizon controls what information a router will send out through a
particular interface. In short, a router will not send route information that it
8. Explain that link-state packets (LSPs), the packets used to send out LSAs, allow every
10. Explain that routers using link-state protocols must be configured with more memory
11. Use Table 7-2 to summarize the main characteristics of both distance-vector and link-
state routing protocols.
Teaching
Tip
For smaller-scale internetworks, distance-vector routing protocols such as RIP
and IGRP are typically used instead of OSPF.
Quick Quiz 1
1. ____ is the number of routers a packet must pass through to reach a particular network.
2. ____ is a state where all routers on the internetwork share a common view of the
internetwork routes.
3. ____ are often referred to as count-to-infinity problems because loops, without
preventive measures, will cause packets to bounce around the internetwork infinitely.
4. ____, which are the packets used to send out LSAs, allow every router in the
internetwork to share a common view of the topology of the internetwork.
Routing Information Protocol
1. Define Routing Information Protocol (RIP) as a distance-vector routing protocol that
broadcasts entire routing tables to neighbors every 30 seconds, out of every interface.
2. Mention that the easiest Interior Gateway Protocol to configure is RIPv1. RIP uses hop
4. Mention that RIP is capable of load balancing, but it is susceptible to all the problems
normally associated with distance-vector routing protocols.
Enabling RIP Routing
1. Use Figures 7-9 through 7-11 to explain how to enable RIP routing in your routers.
Configuring RIP Routing for Each Major Network
1. Explain that the network command turns on RIP routing for a network. An individual
2. Define administrative distance as a value used to determine the reliability of the
information regarding a particular route. Administrative distances range from 0–255.
Show ip protocol and debug ip rip Commands
1. Mention that both commands are used to monitor RIP.
3. Explain that a route is considered invalid if six consecutive update intervals pass
without an update from that route.
5. Explain that the debug ip rip command displays real-time rip updates being sent
and received and places very high processing demands on your router, which could
Interior Gateway Routing Protocol
Teaching
Tip
Read more about RIP at:
http://en.wikipedia.org/wiki/Routing_Information_Protocol.
1. Define IGRP as a proprietary distance-vector routing protocol created by Cisco to solve
some of the problems associated with RIP.
2. Explain that a larger hop-count metric allows IGRP to be used on larger networks.
4. Explain that the default metrics for IGRP are bandwidth and delay only. The metrics
that can be configured for IGRP are:
a. Hops—Number of routers between source and destination networks
b. Load—The load on a link in the path
Teaching
Tip
IGRP is no longer supported on newer versions of the Cisco IOS.
Static Routing
1. Mention that some networks are so small that using a routing protocol creates
unnecessary traffic and an inefficient use of router processor resources.
3. Mention that static routes are configured by a network administrator using the ip
Adding Static Routes
1. Use Figure 7-18 to describe how to add static routes using the ip route command.
Teaching
Tip
Static routes are very powerful, as they allow administrators complete control
over path selection. In addition, they use less bandwidth, less memory, and fewer
CPU resources than routing protocols.
2. Explain that the ip route command allows you to configure an administrative
3. Mention that if you configure a default route, all packets that are not defined
specifically in your routing table will go to the specified interface for the default route.
4. Define a default route as a type of static route that the administrator configures. Default
routes are sometimes called quad zero routes. A default route is used only if no other
5. Explain that you can use the ip default–network command or the ip route
0.0.0.0 0.0.0.0 command to configure a default route.
Quick Quiz 2
1. ____ is a distance-vector routing protocol that broadcasts entire routing tables to
neighbors every 30 seconds, out of every interface.
2. ____ is a value used to determine the reliability of the information regarding a particular
route.
3. The ____ is the time at which a route will be totally removed from the routing table if
no updates are received.
4. Networks with one route to the Internet are called ____.
Class Discussion Topics
1. What are the main problems with Interior Gateway Protocols (IGPs)?
2. What are the advantages and disadvantages of using static routing?
Additional Projects
1. Ask your students to read more about the Internetwork Packet Exchange/Sequenced
2. Ask your students to read more about the Open Shortest Path First (OSPF) link-state
routing protocol and write a report explaining its main characteristics. They may use the
following link as a starting point:
Additional Resources
2. NetWare Protocols
4. Internet protocol suite
6. Interior Gateway Routing Protocol (IGRP)
Key Terms
➢ administrative distance A value used to determine the reliability and desirability of a
particular routing table update.
➢ defining a maximum A technique used with distance-vector routing protocols to
prevent packets from bouncing infinitely throughout an internetwork by setting a
maximum hop count.
➢ distance-vector A routing protocol that functions by broadcasting the entire routing
table periodically to all connected neighbors; examples include RIP and IGRP.
➢ hold-down timer A technique used to stop routing loops in which updates from an
inferior source are not allowed for a certain interval. Used by routers to stabilize routing
tables and to prevent erroneous routing table updates.
➢ hop count A count of the number of routers a packet must pass through to reach a
destination network.
➢ link-state advertisements (LSAs) Routing information packets used by link-state
routing protocols to advertise their local network link information to neighbor routers in
an internetwork.
➢ link-state packets (LSPs) Packets used to send out link-state advertisements.
➢ logical addresses Layer 3 addresses (also referred to as Network layer addresses) that
pass between multiple networks.
➢ routing by rumor The learning of routes through secondhand information, and not
directly from the router experiencing the change. Routing by rumor is characteristic of
distance-vector routing protocols.
➢ Routing Information Protocol (RIP) A distance-vector routing protocol that uses hop
