Chapter 3 - Ethernet Basics

Question 1

Frames

Answer 1

Operate at Layer 2 and use MAC addresses for destination and source

Question 2

Packets

Answer 2

Operate at Layer 3 and use IP addresses for destination and source

Question 3

The five fields of a basic ethernet frame

Answer 3

Destination Address
Source Address
Type
Data
Frame Check Sequence (FCS)

Question 4

Preamble

Answer 4

Added to frame by sending NIC
Gives receiving NIC time to realize a frame is coming and to know exactly where it starts
7 byte series of alt. 1s and 0s

Question 5

Size of MAC Address

Answer 5

48-bit (6 byte)

Question 6

Type field

Answer 6

Helps receiving computer interpret the frame contents at a very basic level (IPv4 or IPv6 for example)
Does NOT tell you if the frame carries higher level data such as an email message or web page

Question 7

Data field

Answer 7

Contains whatever payload the frame carries

Question 8

Minimum ethernet frame size

Answer 8

64 bytes

Question 9

Pad

Answer 9

Extra data added to ethernet frame if it contains less than the minimum requirement of 64 bytes

Question 10

FCS

Answer 10

Frame Check Sequence
Used to “recognize when bad things happen to good data”
Creating using Cyclic Redundancy Check (CRC) to ensure data arrives correctly

Question 11

CRC

Answer 11

Cyclic Redundancy Check
When ethernet frame sent, sending machine runs this math formula and attaches the result as the Frame Check Sequence (FCS)
The receiving computer then performs the same math and if the answers don’t match, the frame is dropped

Question 12

NICs that can only communicate in one direction at a time run in ___

Answer 12

Half-duplex mode

Question 13

NICs that can send and receive at the same time run in ___

Answer 13

Full-duplex mode

Question 14

RJ-45 Connector

Answer 14

Plastic connector with 8 pins. Each pin connects to a single wire inside the cable
Enables devices to put voltage on the individual wires within the cable

Question 15

An RJ-45 connector is sometimes called a ___, and the act of installing it on the end of UTP cable is called ___

Answer 15

Crimp
Crimping

Question 16

CSMA/CD

Answer 16

Carrier-Sense Multiple Access with Collision Detection
Was used on Ethernet networks to determine which computer should use a shared cable at a given moment to attempt to avoid collisions

Question 17

Carrier Sense

Answer 17

Each node using a network examines cable before sending data frame. If another machine is using network, waits a few milliseconds, rechecks, and if it detected no traffic sent out its frame

Question 18

Multiple Access

Answer 18

All machines have equal access to the wire

Question 19

Reasons to use more than one switch

Answer 19

More nodes than available ports
Physical distance requirements
Fault tolerance

Question 20

Uplink Ports

Answer 20

Enable you to connect two switches using a straight-through cable
Older switches had a dedicated uplink port, modern switches autosense when another switch is plugged in

Question 21

MDI-X

Answer 21

Auto-Medium-Dependent Interface Crossover
Technical term for an uplink port and the autosensing feature of ports in modern switches

Question 22

Crossover Cable

Answer 22

Reverses the sending and receiving pairs on one end of the cable allowing switches to hear each other
Not necessary in modern switches

Question 23

Spanning Tree Protocol

Answer 23

Adopted to eliminate the problem of accidental switching loops
Uses special frames called BPDUs and a Root Bridge to prevent loops from happening in the first place

Question 24

BPDU

Answer 24

Bridge Protocol Data Unit
Frames used in Spanning Tree Protocol to communicate with other switches to prevent loops from happening

Question 25

Root Bridge

Answer 25

One switch is elected as Root Bridge which acts as the center of the Spanning Tree Protocol universe
Each switch then uses the root bridge as a reference point to maintain a loop-free topology

Question 26

(TCN) BPDU

Answer 26

Topology Change Notification BPDU
Go into effect if a link or device goes down so that switches can reroute around the failed device/interface