Lesson 4 - Ethernet Technology

Question 1

1973

Answer 1

The genesis of Ethernet was 1973, when this technology was developed by Xerox Corporation

Question 2

IEEE 802.3

Answer 2

n general, you can use the term IEEE 802.3 interchangeably with the term Ethernet. However, be aware that these technologies have some subtle distinctions. For example, an Ethernet frame is a fixed-length frame, whereas an 802.3 frame length can vary

Question 3

10BASE5

Answer 3

The 10 in 10BASE5 referred to network throughput, specifically 10Mbps (that is, 10 million [mega] bits per second). The BASE in 10BASE5 referred to baseband, as opposed to broadband, as discussed in Lesson 2, “The OSI Reference Model.” Finally, the 5 in 10BASE5 indicated the distance limitation of 500 meters. The cable used in 10BASE5 networks, as shown in Figure 4-1, was a larger diameter than most types of media. In fact, this network type became known as thicknet.

Question 4

10BASE2

Answer 4

you might conclude that 10BASE2 was a 10Mbps baseband technology with a distance limitation of 200 meters. That is almost correct. However, 10BASE2’s actual distance limitation was 185 meters. The cabling used in 10BASE2 networks was significantly thinner and therefore less expensive than 10BASE5 cabling. As a result, 10BASE2 cabling, as shown in Figure 4-2, was known as thinnet or cheapernet.

Question 5

10BASE-T

Answer 5

The 10Mbps version of Ethernet that relied on UTP cabling, an example of which is provided in Figure 4-3, is known as 10BASE-T, where the T in 10BASE-T refers to twisted-pair cabling.

Question 6

How many frames on ethernet segment at a time?

Answer 6

Ethernet permits only a single frame to be on a network segment at any one time

Question 7

carrier-sense multiple access/collision detection (CSMA/CD)

Answer 7

The procedure used by Ethernet to decide whether it is safe to transmit, detect collisions, and retransmit if necessary

Question 8

CSMA/CD

Answer 8

Carrier sense: A device attached to an Ethernet network can listen to the wire, prior to transmitting, to make sure that a frame is not being transmitted on the network segment.
Multiple access: Unlike a deterministic method of network access (for example, the method used by Token Ring), all Ethernet devices simultaneously have access to an Ethernet segment.
Collision detection: If a collision occurs (perhaps because two devices were simultaneously listening to the network and simultaneously concluded that it was safe to send), Ethernet devices can detect that collision and set random back-off timers. After each device’s random timer expires, it again tries to transmit its data.

Question 9

CSMA/CA

Answer 9

This technology is common in wireless networks and was made famous by Token Ring in early LANs.

Question 10

Standard Ethernet

Answer 10

10Mbps: 10 million bits per second (that is, 10 megabits per second)

Question 11

Fast Ethernet

Answer 11

100Mbps: 100 million bits per second (that is, 100 megabits per second)

Question 12

Gigabit Ethernet

Answer 12

1Gbps: 1 billion bits per second (that is, 1 gigabit per second) (1000 Mbps)

Question 13

10-Gigabit Ethernet

Answer 13

10Gbps: 10 billion bits per second (that is, 10 gigabits per second)

Question 14

100-Gigabit Ethernet

Answer 14

100Gbps: 100 billion bits per second (that is, 100 gigabits per second)

Question 15

Five nines of availability

Answer 15

If a system has five nines of availability, it is up and functioning 99.999 percent of the time, which translates to only about 5 minutes of downtime per year.

Question 16

Spanning Tree Protocol

Answer 16

To improve network availability at Layer 2, many networks have redundant links between switches. However, unlike Layer 3 packets, Layer 2 frames lack a Time-to-Live (TTL) field. As a result, a Layer 2 frame can circulate endlessly through a looped Layer 2 topology. Fortunately, IEEE 802.1D Spanning Tree Protocol (STP) allows a network to physically have Layer 2 loops while strategically blocking data from flowing over one or more switch ports to prevent the looping of traffic.

Question 17

IEEE 802.1D

Answer 17

Spanning Tree Protocol (STP)

Question 18

If a nondesignated port needs to transition to the forwarding state, it does not do so immediately. Rather, it transitions through the following states:

Answer 18

Blocking: The port remains in the blocking state for 20 seconds by default. During this time, the nondesignated port evaluates BPDUs in an attempt to determine its role in the spanning tree.

Listening: The port moves from the blocking state to the listening state and remains in this state for 15 seconds by default. During this time, the port sources BPDUs, which inform adjacent switches of the port’s intent to forward data.

Learning: The port moves from the listening state to the learning state and remains in this state for 15 seconds by default. During this time, the port begins to add entries to its MAC address table.

Forwarding: The port moves from the learning state to the forwarding state and begins to forward frames

Question 19

link aggregation

Answer 19

To help alleviate congested links between switches, you can (on some switch models) logically combine multiple physical connections into a single logical connection, over which traffic can be sent. This feature, as illustrated in Figure 4-19, is called link aggregation.

Question 20

IEEE 802.3ad standard

Answer 20

Link Aggregation Control Protocol (LACP)

Question 21

IEEE 802.3af

Answer 21

PoE Power over Ethernet. IEEE 802.3af standard can supply a maximum of 15.4W (watts) of power

However, a more recent standard, IEEE 802.3at, offers as much as 32.4W of power, enabling PoE to support a wider range of devices

Question 22

Port Mirroring

Answer 22

port mirroring feature, which makes a copy of traffic seen on one port and sends that duplicated traffic out another port (to which a network sniffer could be attached)

Question 23

User Authentication

Answer 23

For security purposes, some switches require users to authenticate themselves (that is, provide credentials, such as a username and password, to prove who they are) before gaining access to the rest of the network. A standards-based method of enforcing user authentication is IEEE 802.1X.

Question 24

IEEE 802.1X

Answer 24

A standards-based method of enforcing user authentication is IEEE 802.1X.

Question 25

Three Primary Components of 802.1X

Answer 25

Supplicant: The device that wants to gain access to the network.

Authenticator: The authenticator forwards the supplicant’s authentication request on to an authentication server. After the authentication server authenticates the supplicant, the authenticator receives a key that is used to communicate securely during a session with the supplicant.

Authentication server: The authentication server (for example, a Remote Authentication Dial In User Service [RADIUS] server) checks a supplicant’s credentials. If the credentials are acceptable, the authentication server notifies the authenticator that the supplicant is allowed to communicate on the network. The authentication server also gives the authenticator a key that can be used to securely transmit data during the authenticator’s session with the supplicant.

Question 26

Ethernet

Answer 26

Ethernet is a Layer 1 technology developed by Xerox and encompasses a variety of standards that specify various media types, speeds, and distance limitations.

Question 27

collision

Answer 27

A collision occurs when two devices on an Ethernet network simultaneously transmit a frame. Because an Ethernet segment cannot handle more than one frame at a time, both frames become corrupted.

Question 28

carrier-sense multiple access/collision detect (CSMA/CD)

Answer 28

Used on an Ethernet network to help prevent a collision from occurring and to recover if a collision does occur. CSMA/CD is only needed on half-duplex connections.

Question 29

full duplex

Answer 29

This connection allows a device to simultaneously transmit and receive data

Question 30

half duplex

Answer 30

A half-duplex connection allows a device to either receive or transmit data at any one time. However, a half-duplex device cannot simultaneously transmit and receive.

Question 31

virtual LAN (VLAN)

Answer 31

A single broadcast domain, representing a single subnet. Typically, a group of ports on a switch is assigned to a single VLAN. For traffic to travel between two VLANs, that traffic needs to be routed.

Question 32

trunk

Answer 32

In the context of an Ethernet network, this is a single physical or logical connection that simultaneously carries traffic for multiple VLANs. However, a trunk also refers to an interconnection between telephone switches, in the context of telephony.

Question 33

Spanning Tree Protocol (STP)

Answer 33

Defined by the IEEE 802.1D standard, STP allows a network to have redundant Layer 2 connections while logically preventing a loop, which could lead to symptoms such as broadcast storms and MAC address table corruption

Question 34

root port

Answer 34

In an STP topology, every nonroot bridge has a single root port, which is the port on that switch that is closest to the root bridge, in terms of cost

Question 35

designated port

Answer 35

In an STP topology, every network segment has a single designated port, which is the port on that segment that is closest to the root bridge, in terms of cost. Therefore, all ports on a root bridge are designated ports.

Question 36

nondesignated port

Answer 36

In STP terms, nondesignated ports block traffic to create a loop-free topology.

Question 37

link aggregation

Answer 37

As defined by the IEEE 802.3ad standard, link aggregation allows multiple physical connections to be logically bundled into a single logical connection.

Question 38

Power over Ethernet (PoE)

Answer 38

Defined by the IEEE 802.3af and 802.3at standards, PoE allows an Ethernet switch to provide power to an attached device (for example, a wireless access point, security camera, or IP phone) by applying power to the same wires in a UTP cable that are used to transmit and receive data.

Question 39

supplicant

Answer 39

In a network using 802.1X user authentication, a supplicant is the device that wants to gain access to a network.

Question 40

authenticator

Answer 40

In a network using 802.1X user authentication, an authenticator forwards a supplicant’s authentication request on to an authentication server. After the authentication server authenticates the supplicant, the authenticator receives a key that is used to communicate securely during a session with the supplicant.

Question 41

authentication server

Answer 41

In a network using 802.1X user authentication, an authentication server (typically, a RADIUS server) checks a supplicant’s credentials. If the credentials are acceptable, the authentication server notifies the authenticator that the supplicant is allowed to communicate on a network. The authentication server also gives the authenticator a key that can be used to securely transmit data during the authenticator’s session with the supplicant.