The Data Link Layer (TCP/IP)

Question 1

What is the most common protocol to send data across individual links?

Answer 1

Ethernet

Question 2

What is one of the primary purposes of the Data Link Layer?

Answer 2

To abstract away the need for any other layer to care about the physical layer and what hardware is in use

Question 3

What problem did the Ethernet protocol solve?

Answer 3

Collision domains in Hubs

Question 4

What is CSMA/CD?

Answer 4

A technique used to determine when the communications channels are clear and when the device to free to transmit data

Question 5

What is the size of a MAC address and what is it made up of? (Sections excluded)

Answer 5

Its 48 bits long and represented by six groupings of two hexadecimal numbers called Octets

Question 6

In computer networking, what is an Octet?

Answer 6

Any number that can be represented by 8 bits

Question 7

What are the sections of a MAC address?

Answer 7

The first three octets of a MAC address are know as the Organizationally Unique Identifier (OUI), which are assigned to manufacturers by the IEEE. The last three octets determined by the manufacturer

Question 8

What is a Unicast transmission?

Answer 8

A transmission that’s always meant for just one receiving address

Question 9

At the Ethernet level, how does a transmission know whether to send data to one address or multiple?

Answer 9

This is done by looking at a special bit in the destination MAC address. If the least significant bit in the first octet of a destination address is set to zero, it means that Ethernet frame is intended for only the destination address. If the least significant bit in the first octet of a destination address is set to one, it means you’re dealing with a multicast frame

Question 10

What is a Multicast Frame?

Answer 10

A multicast frame is a transmission intended to be sent some MAC addresses on a network

Question 11

What is an Ethernet Broadcast?

Answer 11

An Ethernet transmission sent to every single device on a LAN

Question 12

What is the Ethernet broadcast address literally made up of?

Answer 12

A MAC address but with all Fs

Question 13

What are Data Packets referred to as on the Ethernet level?

Answer 13

Ethernet Frames

Question 14

What is an Ethernet Frame?

Answer 14

An Ethernet frame is a highly structured collection of information presented in a specific order

Question 15

What is the first part of an Ethernet Frame? How large is it?

Answer 15

The preamble, which is 8 bytes long

Question 16

What is the last byte in an Ethernet frame referred to as? What does it do?

Answer 16

Start Frame Delimiter (SFD). It signals to a receiving device that the preamble is over and that the actual frame contents will now follow

Question 17

What is the second part of an Ethernet frame referred to as?

Answer 17

Destination MAC address

Question 18

What is the third part of an Ethernet frame referred to as?

Answer 18

Source MAC address

Question 19

What is the fourth part of an Ethernet frame referred to as? How large is it?

Answer 19

EtherType Field. Its 16 bits long and used to describe the protocol of the contents of the frame

Question 20

What could you also find before an EtherType field in an Ethernet frame? What does it do?

Answer 20

a VLAN header, which indicates that the frame itself is what’s called a VLAN frame. If a VLAN header is present, the EtherType field will follow

Question 21

What is VLAN on an Ethernet frame?

Answer 21

Virtual LAN (VLAN) is a technique that lets you have multiple logical LANs operating on the same physical equipment

Question 22

What is the fifth part of an Ethernet frame referred to as? What does it do? What is the size range?

Answer 22

Payload, which is the actual data being sent, and be between 46 to 1500 bytes long

Question 23

What is the sixth part of an Ethernet frame referred to as? What does it do? What is the size range?

Answer 23

Frame Check Sequence (FCS). Its 4 bytes long and represents a checksum value for the entire frame

Question 24

How is the checksum value of an FCS on an Ethernet frame calculated?

Answer 24

By performing what’s known as a cyclical redundancy check against the frame

Question 25

What is a Cyclical Redundancy Check (CRC)?

Answer 25

A CRC is basically a mathematical transformation that uses polynomial division to create a number that represents a larger set of data. Anytime you perform a CRC against a set of data, you should end up with the same checksum number

Question 26

Does Ethernet report on data recovery?

Answer 26

No