Sem 2 Networking Programming 5-2 Ethernet Switching

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Questions and Answers

What is the advantage of shared memory buffering?

It allows for different data rates on different ports. (correct)

It reduces the size of frames that can be transmitted.

It increases the latency of packet transmission.

It results in more dropped frames.

What is autonegotiation in Ethernet networks?

A feature that enables devices to automatically negotiate the best speed and duplex capabilities. (correct)

A protocol that ensures error-free transmission.

A type of duplex setting that allows only one end to send at a time.

A manual process to configure duplex and speed settings.

What is the main advantage of cut-through switching?

It allows for different data rates on different ports.

It reduces the latency of packet transmission. (correct)

It enables error-free transmission.

It increases the size of frames that can be transmitted.

What is the consequence of duplex mismatch on 10/100 Mbps Ethernet links?

It results in performance issues. Signup and view all the answers

What is the primary purpose of error checking in Ethernet networks?

To detect and correct errors during transmission. Signup and view all the answers

What is the typical application of VoIP in Ethernet networks?

To transmit voice traffic over IP networks. Signup and view all the answers

What is the primary advantage of traffic prioritization in Ethernet networks?

It ensures that critical traffic is transmitted with priority. Signup and view all the answers

What is the characteristic of Gigabit Ethernet ports?

They operate in full-duplex. Signup and view all the answers

In which layer of the OSI model does Ethernet operate?

Data link layer and physical layer Signup and view all the answers

What is the function of the LLC sublayer in Ethernet?

Places information in the frame to identify which network layer protocol is used Signup and view all the answers

What is the purpose of the FCS trailer in an Ethernet frame?

Error detection Signup and view all the answers

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

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

What is the topology used in legacy Ethernet?

Bus Signup and view all the answers

What is the purpose of the MAC sublayer in Ethernet?

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

What is the type of medium used in modern Ethernet LANs?

Full-duplex Signup and view all the answers

What is the function of the MAC address in an Ethernet frame?

Delivering the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN Signup and view all the answers

What happens when a frame is transmitted to an outgoing port in port-based memory?

All frames ahead in the queue must be successfully transmitted first. Signup and view all the answers

What is a limitation of port-based memory?

A single frame can delay the transmission of all frames in memory. Signup and view all the answers

What happens in shared memory?

Frames are deposited into a common memory buffer. Signup and view all the answers

How is buffer memory allocated in shared memory?

The amount of buffer memory required by a port is dynamically allocated. Signup and view all the answers

Which of the following is NOT a characteristic of port-based memory?

Frames are transmitted immediately, regardless of the queue. Signup and view all the answers

What is an advantage of shared memory over port-based memory?

The buffer memory required by a port is dynamically allocated. Signup and view all the answers

What is the main difference between port-based memory and shared memory?

The way frames are stored and transmitted. Signup and view all the answers

Which of the following is a characteristic of port-based memory but NOT of shared memory?

A single frame can delay the transmission of all frames in memory. Signup and view all the answers

What is the process called when a source host determines the destination MAC address associated with an IPv4 address?

Address Resolution Protocol (ARP) Signup and view all the answers

What is the destination MAC address of an Ethernet broadcast frame?

FF-FF-FF-FF-FF-FF Signup and view all the answers

What happens to an Ethernet broadcast frame when it is received by an Ethernet switch?

It is flooded out all Ethernet switch ports except the incoming port. Signup and view all the answers

What is the purpose of the Address Resolution Protocol (ARP)?

To determine the destination MAC address of a packet Signup and view all the answers

What is the destination MAC address of an Ethernet multicast frame when the encapsulated data is an IPv4 multicast packet?

01-00-5E Signup and view all the answers

What happens to an Ethernet multicast frame when it is received by an Ethernet switch that is not configured for multicast snooping?

It is flooded out all Ethernet switch ports except the incoming port. Signup and view all the answers

What is the process called when a source host determines the destination MAC address associated with an IPv6 address?

Neighbor Discovery (ND) Signup and view all the answers

What is the reason why an Ethernet broadcast packet is not forwarded by a router?

Because it is a broadcast packet and routers do not forward broadcast packets Signup and view all the answers

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

It ensures quality of service (QoS) analysis Signup and view all the answers

Which type of switching does not perform error checking on the frame?

Cut-through switching Signup and view all the answers

What is the purpose of discarding frames with errors in networks?

To reduce bandwidth consumption Signup and view all the answers

Which switching technique offers the lowest level of latency?

Fast-forward switching Signup and view all the answers

What is the purpose of buffering on switches?

To store frames before forwarding or when the destination port is busy Signup and view all the answers

Which type of switching stores and performs an error check on the first 64 bytes of the frame?

Fragment-free switching Signup and view all the answers

Why is traffic prioritization necessary in converged networks?

To prioritize VoIP data streams over web-browsing traffic Signup and view all the answers

What is the main disadvantage of fast-forward switching?

It may relay packets with errors Signup and view all the answers

Study Notes

Ethernet Switching

When an error is detected in a frame, the switch discards the frame to reduce bandwidth consumption by corrupt data.
Store-and-forward switching is required for quality of service (QoS) analysis on converged networks, where frame classification for traffic prioritization is necessary.

Cut-Through Switching

In cut-through switching, the switch acts upon the data as soon as it is received, even if the transmission is not complete.
The switch buffers just enough of the frame to read the destination MAC address and determine to which port it should forward the data.
Cut-through switching has two variants: fast-forward switching and fragment-free switching.

Fast-Forward Switching

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.

Fragment-Free Switching

Fragment-free switching is a compromise between the high latency and high integrity of store-and-forward switching and the low latency and reduced integrity of fast-forward switching.
The switch stores and performs an error check on the first 64 bytes of the frame before forwarding.

Memory Buffering on Switches

An Ethernet switch may use a buffering technique to store frames before forwarding them or when the destination port is busy due to congestion.
There are two methods of memory buffering: port-based memory and shared memory.

Port-Based Memory

Frames are stored in queues that are linked to specific incoming and outgoing ports.
A frame is transmitted to the outgoing port only when all the frames ahead in the queue have been successfully transmitted.

Shared Memory

Deposits all frames into a common memory buffer shared by all switch ports.
The amount of buffer memory required by a port is dynamically allocated.

Ethernet Frames

Ethernet operates in the data link layer and the physical layer.
It is a family of networking technologies defined in the IEEE802.2 and 802.3 standards.

Data Link Sublayers

The 802 LAN/MAN standards, including Ethernet, use two separate sublayers of the data link layer to operate: LLC sublayer and MAC sublayer.

LLC Sublayer

The LLC sublayer places information in the frame to identify which network layer protocol is used for the frame.

MAC Sublayer

The MAC sublayer is responsible for data encapsulation and media access control.
It provides data link layer addressing.

Data Encapsulation

IEEE 802.3 data encapsulation includes the following:
- Ethernet frame
- Ethernet addressing
- Ethernet error detection

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.

Media Access

The IEEE 802.3 MAC sublayer includes specifications for different Ethernet communications standards over various types of media, including copper and fiber.

Duplex and Speed Settings

Two of the most basic settings on a switch are the bandwidth ("speed") and duplex settings for each individual switch port.
It is critical that the duplex and bandwidth settings match between the switch port and the connected devices.
There are two types of duplex settings used for communications on an Ethernet network: full-duplex and half-duplex.

Autonegotiation

Autonegotiation is an optional function found on most Ethernet switches and NICs.
It enables two devices to automatically negotiate the best speed and duplex capabilities.

Broadcast MAC Address

An Ethernet broadcast frame is received and processed by every device on the Ethernet LAN.
It has a destination MAC address of FF-FF-FF-FF-FF-FF in hexadecimal (48 ones in binary).
It is flooded out all Ethernet switch ports except the incoming port.
It is not forwarded by a router.

Multicast MAC Address

An Ethernet multicast frame is received and processed by a group of devices that belong to the same multicast group.
It has a destination MAC address of 01-00-5E when the encapsulated data is an IPv4 multicast packet and a destination MAC address of 33-33 when the encapsulated data is an IPv6 multicast packet.

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Description

Learn about the differences between cut-through switching and store-forward switching in networking. Understand how they handle error detection and quality of service (QoS) analysis.