Chapter 3: Ethernet Basics

Question 1

Define: L2 Ethernet Frame - Destination Address and Source Address Fields

Answer 1

The MAC address of the frame’s recipient and the Mac address of the sending system.

Question 2

Define: L2 Ethernet Frame - Type Field

Answer 2

Helps the receiving system interpret the frame contents at a very basic level, such as what version of IP addressing is used.

Question 3

What is contained in the Ethernet Frame data field?

Answer 3

Contains whatever payload the frame carries.

Question 4

Define: L2 Ethernet Frame - Pad

Answer 4

Brings the data up to the minimum 64 bytes required for an Ethernet frame.

Question 5

Define: L2 Ethernet Frame - Frame Check Sequence (FCS)

Answer 5

The cyclic redundancy check (CRC) value used by the receiving system to check the data for errors.

Question 6

Define: L2 Ethernet Frame - Preamble

Answer 6

A 7-byte series of alternating ones and zeroes followed by a 1-byte start frame delimiter or an 8-byte series of ones and zeroes, that precedes a frame.

Question 7

What is the purpose of a Ethernet frame preamble?

Answer 7

It gives a receiving NIC time to realize a frame is coming and to know where the frame starts.

Question 8

Breakdown the parts of 10BASE-T

Answer 8

10: Refers to the speed. In this case 10 Mbps.

BASE: Refers to the signaling type, baseband.

T: Refers to the type of cable used. In this case twisted pair.

Question 9

Define: Baseband

Answer 9

Means that the cable carries only one signal.

Question 10

What pins on an RJ-45 connector are used by 10BASE-T devices?

Answer 10

Pins 1 and 2 send data, and pins 3 and 6 receive data.

Question 11

What is the wire termination order for 568A twisted pair Ethernet cabling?

Answer 11

From left to right:
1. Green/White
2. Green
3. Orange/White
4. Blue
5. Blue/White
6. Orange
7. Brown/White
8. Brown

Remember “GO”

Question 12

What is the wire termination order for 568B twisted pair Ethernet cabling?

Answer 12

From left to right:
1. Orange/White
2. Orange
3. Green/White
4. Blue
5. Blue/White
6. Green
7. Brown/White
8. Brown

Question 13

10BASE-T Summary:
Speed
Distance
Node Limit
Cable Type

Answer 13

Speed: 10 Mbps
Distance: 100 m
Node Limit: No more than 1024 nodes per hub
Cable Type: Cat 3 or better UTP

Question 14

What is a media converter device?

Answer 14

A device used to interconnect different Ethernet types (ie. twisted pair and fiber-optic).

Question 15

Define: Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)

Answer 15

A system used on Ethernet networks to determine which computer should use a shared cable at a given moment. It is disabled in modern full-duplex networks.

Question 16

Define: Collision Domain

Answer 16

A group of nodes that have the capability of sending frames at the same time as each other, resulting in collisions.

Question 17

Define: Switches

Answer 17

A Layer 2 device that filters network traffic by using MAC addresses and port mapping. Each port on a switch is its own collision domain. Switches send all broadcast messages to all the ports (except the port on where it came from). Switched networks are broadcast domains.

Question 18

How do you connect older technology switches?

Answer 18

Either by an uplink port or a crossover cable.

Question 19

How do you connect two switches using an uplink port?

Answer 19

You use a straight-through cable inserted into the uplink port of one switch with the other end inserted into a regular port on the other switch.

Modern switches do not have a dedicated uplink port.

Question 20

How do you connect two switches using a crossover cable?

Answer 20

Insert the crossover cable to a regular port on each switch. The crossover cable allows the switches to hear each other.

Question 21

Define: Crossover Cable

Answer 21

A twisted pair cable where one end is terminated with 568A and the other is terminated with 568B.

Question 22

Define: Auto-Medium-Dependent Interface Crossover (MDI-X)

Answer 22

The technical term for an uplink port and the auto-sensing features of ports in modern switches.

Question 23

What does Spanning Tree Protocol (STP) do, and what special type of frame does it use for communication between switches?

Answer 23

STP eliminates the problem of accidental switching loops by electing one switch as the root bridge. Bridge protocol data units (BPDUs) are the frames used to communicate between switches.

Question 24

What protocol replaced STP?

Answer 24

Rapid Spanning Tree Protocol (RSTP)