Ethernet

Question 1

What layers do Ethernet operate in?

Answer 1

Data Link(Layer 2) and Physical layer(Layer 1)

Question 2

Which two acronyms represent the data link 802.11 sublayers that Ethernet relies upon to operate?

Answer 2

Logical Link Control (LLC) and MAC

Question 3

What is the minimum Ethernet frame size?

Answer 3

64 bytes

Question 4

What is the maximum Ethernet frame size?

Answer 4

1518 bytes ~ 1500 bytes

Question 5

What are the frames that are less than 64 bytes called?

Answer 5

“Collision fragment” or “runt frame”. They are automatically discarded by receiving stations.

Question 6

What are the frames called that are greater than 1518 bytes?

Answer 6

Jumbo or “baby giant frames”.

Question 7

What happens with the frame if the size is less than 64 bytes?

Answer 7

The receiving device drops the frame

Question 8

What happens with the frame if its bigger than 1518 bytes?

Answer 8

The data is either fragmented into smaller frames, or dropped.

Question 9

How many bits in a Ethernet MAC address?

Answer 9

48 bits (4 per hexadecimal digit) → 6 bytes

Question 10

Who establishes the rules for the MAC address?

Answer 10

IEEE

Question 11

What are the two portions of the MAC address?

Answer 11

OUI (Organizationally Unique Identifier) and a vendor assigned code (for the NIC). 24 bits each.

Question 12

Why was MAC addresses created?

Answer 12

MAC addresses were created to identify the actual

source and destination

Question 13

What does a device do when forwarding a message to an Ethernet network?

Answer 13

Attaches the source and destination MAC address into a header.

Question 14

How does a switch build its MAC address table?

Answer 14

• The switch examine all incoming frames for a new source MAC info to learn
• MAC address unknown? → Add to table + port number
• MAC address already exist? → Refresh timer for it (The switch keeps an entry in the table for 5 minutes by default)

Question 15

What is the process for forwarding destination MAC address?

Answer 15

Destination MAC address in table? → Send it to specific port

Destination MAC address NOT in table? → Send the frame as broadcast

Question 16

What are the 2 forwarding methods?

Answer 16

Store-and-forward - The switch stores the entire frame in internal memory and check the frame for errors before forwarding the frame to its destination. Bad frames are discarded.

Question 17

What is Auto-MDIX(Automatic medium-dependent interface crossover)

Answer 17

The switch detects the type of cable attached to the port and configures accordingly.

Question 18

What is ARP?

Answer 18

ARP(Address Resolution Protocol) is a protocol used for discovering MAC addresses linked to IPv4 IP-addresses in a network.

Question 19

How does ARP work?

Answer 19

ARP broadcasts a request packet to all the machines on the LAN and asks if any of the machines are using that particular IP address. When a machine recognizes the IP address as its own, it sends a reply so ARP can update the cache for future reference and proceed with the communication.