CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 2-1
Chapter 2
Network Devices
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 2-2
Lecture Notes
Overview
Many devices help control and extend the usable size of a growing network. These devices
have a wide variety of functions and are added to networks to allow a greater number of
computers to exist on the network; to extend the usable distance of the network; to segment,
or localize, traffic on the network; to subdivide the network so problems are easier to
isolate; and to join existing networks together. In this chapter, you will learn about the
different devices that can be used to accomplish these objectives. The devices include
repeaters, hubs, bridges, switches, routers, brouters, wireless access points, and gateways.
In addition, you will learn about Ethernet, which is the most prolific network technology in
use on LANs today. This chapter will explain a variety of Ethernet operations including
CSMA/CD, Fast Ethernet, Gigabit Ethernet, and half- and full-duplex communications.
Chapter Objectives
• Explain the uses, advantages, and disadvantages of repeaters, hubs, wireless access
points, bridges, switches, and routers
• Define the standards associated with wireless media
• Explain basic wireless connection parameters, security, and troubleshooting
• Define network segmentation
• Explain network segmentation using bridges, switches, routers, brouters, and gateways
• Explain Ethernet operations
• Define Fast Ethernet and Gigabit Ethernet
Teaching Tips
Repeaters
2. Define attenuation as the degradation of signal clarity. Repeaters work against
attenuation by repeating signals that they receive on a network, typically cleaning and
regenerating the digital transmission in the process. Use Figure 2-1 to illustrate your
explanation.
Teaching
Tip
Learn more about repeaters at: http://en.wikipedia.org/wiki/Repeater.
3. Note that on analog networks, devices that boost the signal are called amplifiers. These
4. Mention that repeaters work in the Physical layer (layer 1).
6. Explain that some repeaters can be used to connect two physically different types of
cabling. Use Figure 2-2 to illustrate your explanation.
Hubs
1. Define a hub as a generic connection device used to tie several networking cables
together to create a link between different stations on a network.
2. Explain that active hubs amplify or repeat signals that pass through them. A passive hub
merely connects cables on a network and provides no signal regeneration.
Teaching
Tip
Refer your students to
http://compnetworking.about.com/cs/internetworking/g/bldef_hub.htm for
additional information about network hubs.
3. Explain that topology refers to the physical layout of network cable and devices. Use
Figure 2-3 to illustrate your explanation.
Advantages and Disadvantages of Repeaters and Hubs
1. Describe the following advantages of using repeaters and hubs in your network:
2. Describe the following disadvantages of using repeaters and hubs in your network:
a. Repeaters and hubs cannot connect different network architectures, such as
3. Explain that repeaters and hubs do not reformat data structures, so they cannot connect
4. Mention that repeaters do not segment a network. Frames that are broadcast on a given
segment may collide. Devices that “see” the traffic of other devices are said to be on the
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Wireless Access Points
1. Explain that wireless access points provide cell-based areas where wireless clients such
2. Explain that wireless access points operate at the Physical and Data Link layers of the
OSI model. In most respects, a wireless access point functions exactly like a hub.
Teaching
Tip
Each access point and wireless client must contain a radio transceiver that
matches the wireless technology on the network or there can be no
communications between them.
Wireless Standards and Organizations
1. Use Table 2-1 to describe various wireless standards and organizations.
Wireless Network Components
1. Explain that wireless clients can connect and communicate directly with each other in
ad hoc mode. In this mode, there is no access point, which is not typical.
2. Explain that commonly, wireless clients attach wirelessly to an access point in
4. Explain that more typically, WLANs involve multiple access points connected to
Wireless Connectivity
1. Mention that access points typically broadcast their network name, also known as the
Service Set Identifier (SSID).
2. Explain that when wireless clients are powered on, they begin scanning the airspace for
available access points. They detect the broadcasted SSID of the various access points
3. Explain that when the SSID is not broadcasted, wireless clients must already be
configured with the correct SSID. The client will send out a probe request with the
configured SSID, and the access point with that SSID configured will allow the client to
associate.
Teaching
Tip
Sometimes, access points are configured not to broadcast their SSID. This is a
safety feature, although a very weak one.
Wireless Security Measures
1. Mention that while security is always necessary in WLANs due to the broadcast nature
3. Explain that workspace situations call for security that not only requires the client
4. Mention that the 802.1x is used at the physical layer to block ports, and the Extensible
Authentication Protocol (EAP) is used at layer 2 to transfer the authentication frames.
Wireless Troubleshooting
1. Describe the following steps for adding a WLAN to your LAN:
a. Make sure your wired LAN is working.
2. Explain that as the number of users on the WLAN increases, each user’s individual
bandwidth will decrease.
3. Describe the following problems that are particular to 802.11 networks:
a. Interference may occur from too much overlap of one access point’s cell range
onto another.
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Advantages and Disadvantages of Wireless Access Points
1. Describe the following advantages of using 802.11 on your network:
a. Wireless devices provide the ability to work anywhere within range of your
2. Describe the following advantages of using 802.11 on your network:
a. Wireless introduces serious security concerns into the network environment.
b. 802.11 provides much less bandwidth than wired devices.
Network Segmentation
1. Define segmentation as the breaking down of a single heavily populated network
2. Define segment as a part of a network that is divided logically or physically from the
rest of the network.
3. Explain that network problems occur when network administrators place too many
Quick Quiz 1
1. ____ usually refers to the physical layout of network cable and devices.
2. Devices that “see” the traffic of other devices are said to be on the same ____ as those
devices.
3. ____ provide cell-based areas where wireless clients such as laptops and PDAs can
connect to the network by associating with the access point.
4. A(n) ____ is a part of a network that is divided logically or physically from the rest of
the network.
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Bridges
1. Explain that bridges operate at the Data Link layer of the OSI model. They filter traffic
2. Mention that bridges reduce network traffic by keeping local traffic on the local
segment.
3. Define a broadcast frame as a frame destined for all computers on the network.
Teaching
Tip
The bridge functions like a repeater in that it listens to incoming frames and
repeats them on other segments. The only real difference is that it actually reads
the MAC address and chooses whether to repeat or discard a frame.
Transparent Bridges
1. Explain that transparent bridges are also called learning bridges because they build a
2. Explain that a transparent bridge uses the source MAC addresses to determine which
Source-Routing Bridges
1. Explain that source-routing bridges rely on the source of the frame transmission to
2. Mention that the source includes the routing information returned by its explorer frames
in the frame sent across the network. The bridge uses this information to build its table.
Translation Bridges
1. Explain that translation bridges can connect networks with different architectures, such
as Ethernet and Token Ring. These bridges appear as transparent bridges to an Ethernet
host and as source-routing bridges to a Token Ring host.
Advantages and Disadvantages of Bridges
1. Describe the following advantages of using bridges:
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 2-8
2. Describe the following disadvantages of using bridges:
a. Because bridges do more than repeaters by viewing MAC addresses, the extra
3. Explain that a broadcast storm occurs when two or more stations engage in the
transmission of excessive broadcast traffic.
Teaching
Tip
While some broadcasting is normal on networks, excessive broadcasting due to
errors or malfunctioning NICs can seriously erode network performance and
even bring a network to a halt.
Switches
1. Explain that switches operate at the Data Link layer of the OSI model and increase
2. Explain that a switch opens a virtual circuit between the source and the destination. This
3. Mention that when two machines have a virtual circuit, they do not have to share the
4. Mention that when machines must share a wire and compete for available bandwidth
with other machines, they experience contention.
Teaching
Tip
Switches filter based on MAC addresses and build tables in memory just like
bridges, but the switching table will have a mapping of switch port number to
MAC address instead of bridge segment number to MAC address.
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Advantages and Disadvantages of Switches
1. Describe the following advantages of using switches:
a. Switches increase available network bandwidth.
2. Describe the following disadvantages of using switches:
a. Switches are significantly more expensive than bridges.
Routers
1. Explain that routers operate at the Network layer of the OSI model and provide filtering
2. Define internetworks as networks connected by multiple routers.
3. Mention that routers are similar to switches and bridges in that they segment a network
Physical vs. Logical Addresses
1. Explain that the MAC address is found at the Data Link layer of the OSI model and
2. Explain that the IP address is the logical address when TCP/IP is used on an
Advantages and Disadvantages of Routers
1. Describe the following advantages of using routers:
a. Routers can connect different network architectures, such as Ethernet and Token
2. Describe the following disadvantages of using routers:
a. Routers work only with routable network protocols; most but not all protocols
3. Use Figure 2-9 to show how to use a router to connect a network to the Internet.
Brouters
1. Define a brouter as a hybrid device that functions as both a bridge for nonroutable
2. Mention that a brouter operates at both the Data Link and Network layers and can
Gateways
1. Explain that a gateway is usually a combination of hardware and software that translates
between different protocol suites.
2. Explain that packets must be rebuilt not just at the lower levels but at the very upper
3. Mention that gateways have the most negative effect on network performance.
Ethernet Operations
802.3 in the early 1980s.
2. Mention that today, Ethernet is the most commonly implemented media access method
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CSMA/CD
1. Explain that Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is
2. Mention that after each transmitted signal, each station must wait a minimum of 9.6
3. Explain that two stations could listen to the wire simultaneously and not sense a carrier
4. The first station to detect the collision transmits a 32-bit jam signal that tells all other
5. Define a collision domain as the physical area in which a frame collision might occur.
Fast Ethernet
1. Explain that Fast Ethernet (100BaseT) uses the same network access method
2. Mention that when you upgrade from 10BaseT to Fast Ethernet, all the network cards,
Gigabit Ethernet
1. Explain that Gigabit Ethernet (1000BaseX) is the next iteration of Ethernet, increasing
3. Mention that 10 Gigabit Ethernet (10GBaseX, 10GbE or 10GigE) is the fastest of the
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Half- and Full-Duplex Communications
1. Explain that in half-duplex communications, devices can send and receive signals, but
2. Mention that most Ethernet networks can use equipment that supports half- and full-
3. Describe the following benefits of using full-duplex:
a. Time is not wasted retransmitting frames, because there are no collisions.
Quick Quiz 2
1. Networks connected by multiple routers are called ____ because they create a larger
network of interconnected, smaller networks.
2. A(n) ____ functions as both a bridge for nonroutable protocols and a router for routable
protocols.
3. Fast Ethernet is defined under the IEEE ____ standard.
4. In ____ communications, devices can send and receive signals, but not at the same time.
Class Discussion Topics
1. What are the benefits of implementing a WLAN?
2. What are the advantages and disadvantages of using hybrid devices such as brouters?
Additional Projects
1. Ask your students to read more about Wired Equivalent Privacy (WEP) and write a
2. CSMA/CA is used in 802.11 based wireless LANs. Ask your students to read more
about CSMA/CA and write a report explaining its most important characteristics. They
should include the main differences between CSMA/CA and CSMA/CD used with
Ethernet.
Additional Resources
1. Network hub
2. Wireless access point
3. SSID – Service Set Identifier
6. Network switch
Key Terms
➢ 100BaseFX A Fast Ethernet implementation over multimode fiber-optic cabling. The
maximum segment length is 412 meters.
copper cabling to achieve 1000 Mbps.
➢ 1000BaseLX An IEEE 802.3z Gigabit Ethernet implementation that uses single-mode
fiber to achieve 1000 Mbps.
➢ 1000BaseSX An IEEE 802.3z Gigabit Ethernet implementation that uses multimode
fiber to achieve 1000 Mbps.
➢ 1000BaseT An IEEE 802.3ab Gigabit Ethernet implementation that uses all four pairs
of Category 5 or better UTP cable to achieve 1000 Mbps.
➢ active hub A device that connects multiple nodes and/or networks, is connected to
external power, and repeats and regenerates signals on a network.
➢ Basic Service Set (BSS) A wireless network with only one access point connected to a
switch.
➢ bridge A device that operates at the Data Link layer, used to filter traffic between
network segments by evaluating the MAC address of packets that are sent to it.
➢ broadcast A frame meant for the entire network.
perform the backoff algorithm.
➢ carrier signal A transmitted electromagnetic pulse or wave on the network wire that
indicates a transmission is in progress.
➢ collision domain In Ethernet networking, a single segment on a network. Any station
on the same physical segment or separated by a repeater is in the same collision domain.
➢ Extensible Authentication Protocol (EAP) Works with 802.1x to carry the
authentication information between the user, the access point, and the security server.
➢ full-duplex A connection that allows communication in two directions at once;
common telephone connections are typically full-duplex because people can talk and
listen at the same time.
➢ hub An active or passive device that connects network segments. Passive hubs are
connection points; active hubs repeat and regenerate signals.
➢ IEEE 802.1x The IEEE standard that defines port switching designed to shut down a
switch port to all frames unless they are authentication frames.
➢ IEEE 802.11 The IEEE standard that defines wireless networking in the unlicensed
➢ infrastructure mode A wireless mode in which the access point is wired back into a
switch so that the client has access to the LAN and WAN, not just the WLAN.
➢ interframe gap (IFG) The time required between the transmission of data frames on
the network: 9.6 microseconds.
➢ interpacket gap (IPG) See interframe gap.
Bandwidth is not shared as it is through hubs.
➢ network access method The process by which network interface cards and devices
communicate data on a network; an example is CSMA/CD. Also known as media
access method.
➢ node A connection point or junction on the network. A node can be a terminal or
➢ router A device that connects multiple segments, subdivides a network, filters
broadcast traffic, and maintains a routing table. A router uses the logical address to
move data packets from point to point.
➢ segment (noun) A section of a network that has been subdivided by routers, switches,
or bridges.
two points.
➢ Token Ring A networking method developed by IBM that organizes the network into a
physical or logical ring. The token is a logical device, and because stations may only
broadcast on the network when they have the token, traffic does not collide.
➢ topology The physical layout of network components. The topology can take the form