4.5.3 Ethernet Switching Quiz and Flashcards

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Questions and Answers

Which layer of the OSI model does Ethernet operate in?

Data link layer and physical layer (correct)

Session layer

Network layer

Transport layer

What is the primary function of the LLC sublayer?

Identifying network layer protocols (correct)

Media access control

Providing data link layer addressing

Data encapsulation

What is the responsibility of the MAC sublayer?

Identifying network layer protocols

Data encapsulation and media access control (correct)

Providing data link layer addressing

Providing physical layer addressing

Which standard defines the Ethernet technology?

IEEE 802.2 and 802.3 Signup and view all the answers

What is the primary function of a switch in a switched network?

Forwarding frames Signup and view all the answers

What is the term for the process of a switch building its MAC address table?

MAC address learning Signup and view all the answers

What is the primary function of the data link layer?

Data encapsulation and media access control Signup and view all the answers

What is the term for the division of the data link layer into two sublayers?

Data link sublayers Signup and view all the answers

What is the purpose of the frame check sequence (FCS) trailer in an Ethernet frame?

To detect errors in the frame Signup and view all the answers

What is the minimum size of an Ethernet frame?

64 bytes Signup and view all the answers

What happens to frames less than 64 bytes in length?

They are automatically discarded Signup and view all the answers

What is the function of the MAC sublayer in IEEE 802.3?

To specify Ethernet communications standards Signup and view all the answers

What is the access method used in legacy Ethernet over a half-duplex medium?

Carrier sense multiple access with collision detection (CSMA/CD) Signup and view all the answers

What is the maximum size of an Ethernet frame?

1518 bytes Signup and view all the answers

What happens to frames with more than 1500 bytes of data?

They are considered jumbo or baby giant frames Signup and view all the answers

Why are dropped frames likely to occur?

Due to collisions or other unwanted signals Signup and view all the answers

What is the length of an Ethernet MAC address in bytes?

6 bytes Signup and view all the answers

What is the purpose of MAC addressing in an Ethernet LAN?

To provide a method for device identification Signup and view all the answers

How many bits is an Ethernet MAC address?

48 bits Signup and view all the answers

What is the range of hexadecimal values that can be represented by one byte of a MAC address?

00 to FF Signup and view all the answers

Why are leading zeroes always displayed in hexadecimal representation of a MAC address?

To complete the 8-bit representation Signup and view all the answers

What is the notation used to distinguish hexadecimal values from decimal values in documentation?

0x or subscript 16 Signup and view all the answers

What is the number of hexadecimal digits used to express an Ethernet MAC address?

12 hexadecimal digits Signup and view all the answers

What type of Ethernet frames are usually supported by most Fast Ethernet and Gigabit Ethernet switches and NICs?

Jumbo frames Signup and view all the answers

What happens when the MAC address table of the switch contains the destination MAC address?

The switch filters the frame and forwards it out a single port. Signup and view all the answers

What is the main topic of the video 'MAC Address Tables on Connected Switches'?

How switches build MAC address tables and forward frames Signup and view all the answers

What happens when the destination MAC address is not listed in the switch's MAC address table?

The switch sends the frame to the default gateway. Signup and view all the answers

What is the purpose of the lab 'View the Switch MAC Address Table'?

To examine the switch's MAC address table Signup and view all the answers

What is store-and-forward switching?

A method of switching that receives the entire frame and computes the CRC Signup and view all the answers

What is the main topic of the section 'Switch Speeds and Forwarding Methods'?

Switch speeds and forwarding methods Signup and view all the answers

What is the purpose of the MAC address table?

To make forwarding decisions Signup and view all the answers

What happens when the source MAC address is not listed in the switch's MAC address table?

The switch learns the source MAC address and adds it to the table Signup and view all the answers

What happens to a frame with errors in a store-and-forward switching method?

The frame is discarded Signup and view all the answers

What is the primary advantage of cut-through switching?

Low latency Signup and view all the answers

What is the purpose of store-and-forward switching in converged networks?

To provide quality of service analysis Signup and view all the answers

What happens to a frame in a cut-through switching method?

The frame is forwarded before it is entirely received Signup and view all the answers

What is the minimum information required to forward a frame in a cut-through switching method?

Destination MAC address Signup and view all the answers

What is the typical cut-through method of switching?

Fast-forward switching Signup and view all the answers

What is the advantage of store-and-forward switching over cut-through switching?

Error detection and correction Signup and view all the answers

What type of traffic requires priority over web-browsing traffic?

Voice over IP traffic Signup and view all the answers

Study Notes

Ethernet Frames

Ethernet operates in the data link layer and the physical layer.
It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards.
The 802 LAN/MAN standards, including Ethernet, use two separate sublayers of the data link layer to operate:
- LLC Sublayer (IEEE 802.2): Places information in the frame to identify which network layer protocol is used for the frame.
- MAC Sublayer (IEEE 802.3, 802.11, or 802.15): Responsible for data encapsulation and media access control, and provides data link layer addressing.
IEEE 802.3 data encapsulation includes:
- Ethernet frame: The internal structure of the Ethernet frame.
- Ethernet Addressing: The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN.
- Ethernet Error detection: The Ethernet frame includes a frame check sequence (FCS) trailer used for error detection.
The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes.
Any frame less than 64 bytes in length is considered a “collision fragment” or “runt frame” and is automatically discarded.
Frames with more than 1500 bytes of data are considered “jumbo” or “baby giant frames”.

Ethernet MAC Address

An Ethernet MAC address consists of a 48-bit binary value, expressed using 12 hexadecimal values.
MAC addressing provides a method for device identification at the data link layer of the OSI model.
An Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits.
Because a byte equals 8 bits, a MAC address is 6 bytes in length.
When the MAC address table of the switch contains the destination MAC address, it is able to filter the frame and forward out a single port.

The MAC Address Table

A switch builds its MAC address table by learning the source MAC address of incoming frames and associating them with the port on which they were received.
The switch forwards frames based on the content of their MAC address tables.
When the destination MAC address is not listed in the switch’s MAC address table, it sends the frame to the default gateway.
When the source MAC address is not listed in the switch’s MAC address table, it adds the source MAC address to the table.

Switch Speeds and Forwarding Methods

Switches use one of the following forwarding methods for switching data between network ports:
- Store-and-forward switching: Receives the entire frame and computes the CRC. If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. Then the frame is forwarded out of the correct port.
- Cut-through switching: Forwards the frame before it is entirely received. At a minimum, the destination address of the frame must be read before the frame can be forwarded.
Cut-through switching has two variants:
- Fast-forward switching: Offers the lowest level of latency by immediately forwarding a packet after reading the destination address. Because fast-forward switching starts forwarding before the entire packet has been received, there may be times when packets are relayed with errors. The destination NIC discards the faulty packet upon receipt.

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Description

This quiz covers the basics of Ethernet switching in a network, including the Ethernet sublayers, frame fields, and MAC addresses. Learn how Ethernet works in a switched network and how a switch builds a MAC address table.

Ethernet Switching Module 7