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Chapter 6: Routing IP Packets
Core Idea
The core concept here is the information flow between broadcast domains. This builds on the
addressing concepts of Chapter 5 and expands it to allow communication.
Instructor Focus
The focus of this topic should be on how to establish routes between end station networks, ie,
broadcast domains. The central device that must manage this is a router, a networking device
Network+ Exam Objective for this Chapter/Lesson
x 1.3 Explain the characteristics and concepts of routing and switching
Terminology
Make an effort to define the following terms for the designated areas. After defining these,
calling on the students for repeat definitions as you progress through the slide deck will help
them retain the terminology.
Routing Terminology:
x ARP
x TTL
x IGP
x EGP
x Distance vector
x Link state
x Hold-down timer
x Split horizon
x Poison reverse
x OSPF
x IS-IS
x EIGRP
Focus Questions
1) How are source and destination IP addresses used to route traffic through a network?
2) What are sources for routing information used to populate a router’s routing table?
3) How do routed protocols differ from routing protocols?
4) When multiple routing protocols know how to reach a destination network, which route is
chosen?
5) When a single routing protocol knows of multiple routes to reach a destination network, how
is the preferred path (or paths) chosen?
6) What is the distinction between an Interior Gateway Protocol (IGP) and an Exterior Gateway
Protocol (EGP)?
Chapter 6: Network Simulator Activities
x Connecting to the Router’s Console Port
x Configuring an Ethernet Interface on a Router
Icebreaker Discussion
Choose one or both of the following:
1. What is necessary for a router to know where to send a message next?
2. What are some possible sources of address information for a router?
Because this is a preliminary discussion, you should not expect your students to be able to
identify every possible source, but you should push them to discover most of these even if
Icebreaker Activity
1. Given two subdomains connected by a single router, how would a device on one subdomain
contact a device on the other subdomain?
This should be an informal exercise. You can define IP addresses if it helps to get the
example across, but you would then need to identify subdomains and masks, which gets
Main Activities
1. Routing Example
Use the following network to begin the routing exploration.
PC1: 192.168.1.2 /24
PC2: 192.163.6.4 /24
R2: 192.163.6.1 /24
1.) If PC1 wants to communicate with PC2, it must first determine that the destination is
outside of the broadcast domain. It will therefore send the message to its default gateway,
R1. To form the frame, it will need to use ARP to get the MAC address of R1.
2.) R1 receives the packet destined for PC2 and interrogates the IP header, decrementing the
3.) R2 receives the packet destined for PC2, decrementing the TTL value. R2 detects that PC2 is
directly attached to its broadcast domain. It must therefore use ARP to detect the MAC
address of the intended recipient. ARP will use a broadcast frame to everyone first.
However, only PC2 will respond, allowing the router to receive the response and memorize
the actual MAC address of PC2.
PC1: 192.168.1.2 /24
MAC: 1111.1111.1111
PC1: 192.168.1.2 /24
MAC: 1111.1111.1111
PC2: 192.163.6.4 /24
MAC: AAAA.AAAA.AAAA
R2: 192.163.6.1 /24
PC1: 192.168.1.2 /24
MAC: 1111.1111.1111
PC2: 192.163.6.4 /24
MAC: 4444.4444.4444
Once the ARP request is completed, R2 is able to forward the message to PC2 via the broadcast domain
switch SW2 using a unicast frame/packet.
Chapter 6: Additional Network Simulator Activities
x Static and Default Routes
x Configuring Dynamic Routing
x Reading a Routing Table
Quiz Questions
You can ask the following questions either in class for a group discussion or for individual practice. If
you ask them for individual practice, review in class to make sure everyone properly understands
the content.
1. What are the three primary ways in which routing information can be determined by a router?
Directly connected routes: These are where the router has a physical connection directly to the
network.
2. Why is it important for a router to have a metric for determining an optimal route?
PC1: 192.168.1.2 /24
MAC: 1111.1111.1111
PC2: 192.163.6.4 /24
MAC: 4444.4444.4444
3. Briefly define the following routing protocols: RIP, OSPF, and BGP.
RIP: RIP is an Interior Gateway Protocol (IGP) where hop count is the measurement of ideal
4. What is gained by using either split horizon or poison reverse when establishing routes?
