CCNA 1 v7 – ITN v7.02 – Modules 4 – 7: Ethernet Concepts | Practice Online Exam

Copper Cables - horizontal cabling structure and desktop PCs in offices in an enterprise
Fiber optic - backbone cabling in an enterprise and long-haul networks
Wireless - coffee shops and waiting rooms in a hospital

The OSI physical layer provides the means to transport the bits that make up a frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted to the local media.

Fiber-optic cabling supports higher bandwidth than UTP for longer distances. Fiber is immune to EMI and RFI, but costs more, requires more skill to install, and requires more safety precautions.

Throughput usually does not match the specified bandwidth of physical links due to multiple factors. These factors include, the amount of traffic, type of traffic, and latency created by the network devices the data has to cross.

The Ethernet frame includes the source and destination physical address. The trailer includes a CRC value in the Frame Check Sequence field to allow the receiving device to determine if the frame has been changed (has errors) during the transmission.

Wired Ethernet networks use CSMA/CD for media access control. IEEE 802.11 wireless networks use CSMA/CA, a similar method. Media access control defines the way data frames get placed on the media. The controlled access method is deterministic, not a contention-based access to networks. Because each device has its own time to use the medium, controlled access networks such as legacy Token Ring do not have collisions.

The Logical Link Control (LLC) defines the software processes that provide services to the network layer protocols. The information is placed by LLC in the frame and identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to utilize the same network interface and media.

In an extended star topology, central intermediate devices interconnect other star topologies.

Half-duplex communication occurs when both devices can both transmit and receive on the medium but cannot do so simultaneously. Full-duplex communication occurs when both devices can transmit and receive on the medium at the same time and therefore does not require media arbitration. Half-duplex communication is typically contention-based, whereas controlled (deterministic) access is applied in technologies where devices take turns to access the medium.

An Ethernet frame is not processed and is discarded if it is smaller than the minimum (64 bytes) or if the calculated frame check sequence (FCS) value does not match the received FCS value. Auto-MDIX (automatic medium-dependent interface crossover) is Layer 1 technology that detects cable straight-through or crossover types. The source MAC address is not used to determine how the frame is received. CEF (Cisco Express Forwarding) is a technology used to expedite Layer 3 switching.

Partial mesh topologies provide high availability by interconnecting multiple remote sites, but do not require a connection between all remote sites. A mesh topology requires point-to-point links with every system being connected to every other system. A point-to-point topology is where each device is connected to one other device. A hub and spoke uses a central device in a star topology that connects to other point-to-point devices.

All data link layer protocols encapsulate the Layer 3 PDU within the data field of the frame. However, the structure of the frame and the fields that are contained in the header vary according to the protocol. Different data link layer protocols may use different fields, like priority/quality of service, logical connection control, physical link control, flow control, and congestion control.

The trailer in a data-link frame contains error detection information that is pertinent to the frame included in the FCS field. The header contains control information, such as the addressing, while the area that is indicated by the word "data" includes the data, transport layer PDU, and the IP header.

The CRC value in the FCS field of the received frame is compared to the computed CRC value of that frame, in order to verify the integrity of the frame. If the two values do not match, then the frame is discarded.

The data link layer is divided into two sub layers, namely Logical Link Control (LLC) and Media Access Control (MAC). LLC forms a frame from the network layer PDU into a format that conforms to the requirements of the network interface and media. A network layer PDU might be for IPv4 or IPv6. The MAC sub layer defines the media access processes performed by the hardware. It manages the frame access to the network media according to the physical signaling requirements (copper cable, fiber optic, wireless, etc.)

Radio Frequency Interference (RFI) is the interference that is caused by radio transmitters and other devices that are transmitting in the same frequency.

Network cabling include different types of cables:
UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.
STP cable uses four pairs of wires, each wrapped in a foil shield, which are then wrapped in an overall metallic braid or foil.
Coaxial cable uses a copper conductor and a layer of flexible plastic insulation surrounds the copper conductor.
Fiber cable is a flexible, extremely thin, transparent strand of glass surrounded by plastic insulation.

Copper media is widely used in network communications. However, copper media is limited by distance and signal interference. Data is transmitted on copper cables as electrical pulses. The electrical pulses are susceptible to interference from two sources:
Electromagnetic interference (EMI) or radio frequency interference (RFI) - EMI and RFI signals can distort and corrupt the data signals being carried by copper media.
Crosstalk - Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire interfering with the signal in an adjacent wire.

Network cabling include different types of cables:
UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath.
STP cable uses four pairs of wires, each wrapped in a foil shield, which are then wrapped in an overall metallic braid or foil.
Coaxial cable uses a copper conductor and a layer of flexible plastic insulation surrounds the copper conductor.
Fiber cable is a flexible, extremely thin, transparent strand of glass surrounded by plastic insulation.

Crosstalk is a type of noise, or interference that occurs when signal transmission on one wire interferes with another wire. When current flows through a wire a magnetic field is produced. The produced magnetic field will interface the signal carried in the adjacent wire.

The switch forwards a frame with the destination MAC address FF:FF:FF:FF:FF:FF out all ports except the ingress (receiving) port. This is the typical behavior for broadcast frames, as they are intended to be received by all devices within the same local network segment. By forwarding the frame to all ports except the one it came in on, the switch ensures that all devices connected to the same LAN segment have the opportunity to process the broadcasted message or frame.

When a host receives a frame with a destination MAC address it does not recognize (i.e., a MAC address not associated with its own MAC address or a broadcast MAC address), the typical action is for the host to discard the frame.

Hosts in a network typically process frames with destination MAC addresses that match their own MAC address or broadcast addresses. Frames intended for other hosts should not be processed by the receiving host and are simply discarded. This behavior ensures that only the intended recipient processes the frame, reducing unnecessary network traffic and processing overhead on individual hosts.

The host would not send the frame to the switch to update the MAC address table, forward it to the router, or forward it to all other hosts in this scenario.

It implies that the switch updates the timestamp on the existing MAC address table entry when it receives a frame with a known source MAC address. This refreshes the entry to indicate the most recent time the MAC address was active on the network.

When a host receives a frame with a destination MAC address of FF:FF:FF:FF:FF:FF, it typically processes the frame. This MAC address is the broadcast address, and frames with this destination address are intended to be received and processed by all devices on the same local network segment.

In a broadcast frame, the intention is to communicate with all devices on the local network, and it may contain information relevant to all hosts. Therefore, the host processes the frame to determine if it needs to respond or take any action based on the content of the broadcast message.

This is a common behavior in Ethernet networks where broadcast frames are used for various purposes, such as ARP (Address Resolution Protocol) requests or DHCP (Dynamic Host Configuration Protocol) requests.

It implies that the switch updates the timestamp on the existing MAC address table entry when it receives a frame with a known source MAC address. This refreshes the entry to indicate the most recent time the MAC address was active on the network.

When a host receives a frame with a destination MAC address of FF:FF:FF:FF:FF:FF, it typically processes the frame. This MAC address is the broadcast address, and frames with this destination address are intended to be received and processed by all devices on the same local network segment.

In a broadcast frame, the intention is to communicate with all devices on the local network, and it may contain information relevant to all hosts. Therefore, the host processes the frame to determine if it needs to respond or take any action based on the content of the broadcast message.

This is a common behavior in Ethernet networks where broadcast frames are used for various purposes, such as ARP (Address Resolution Protocol) requests or DHCP (Dynamic Host Configuration Protocol) requests.

When a host receives a frame with a destination MAC address it does not recognize (i.e., a MAC address not associated with its own MAC address or a broadcast MAC address), the typical action is for the host to discard the frame.

Hosts in a network typically process frames with destination MAC addresses that match their own MAC address or broadcast addresses. Frames intended for other hosts should not be processed by the receiving host and are simply discarded. This behavior ensures that only the intended recipient processes the frame, reducing unnecessary network traffic and processing overhead on individual hosts.

The host would not send the frame to the switch to update the MAC address table, forward it to the router, or forward it to all other hosts in this scenario.

The switch forwards a frame with the destination MAC address FF:FF:FF:FF:FF:FF out all ports except the ingress (receiving) port. This is the typical behavior for broadcast frames, as they are intended to be received by all devices within the same local network segment. By forwarding the frame to all ports except the one it came in on, the switch ensures that all devices connected to the same LAN segment have the opportunity to process the broadcasted message or frame.

It implies that the switch updates the timestamp on the existing MAC address table entry when it receives a frame with a known source MAC address. This refreshes the entry to indicate the most recent time the MAC address was active on the network.

The two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer are:

1. Provides a mechanism to allow multiple devices to communicate over a shared medium: The MAC sublayer is responsible for controlling access to the shared communication medium, such as an Ethernet segment, to ensure that multiple devices can transmit and receive data without causing collisions. It implements access control mechanisms like CSMA/CD or CSMA/CA.
2. Controls the NIC responsible for sending and receiving data on the physical medium: The MAC sublayer manages the Network Interface Card (NIC) to control the sending and receiving of data frames on the local network segment. It controls how data is placed onto the physical medium, including addressing and frame delimitation.

The other options mentioned, such as placing information in the frame that identifies the network layer protocol, adding Layer 2 control information to network protocol data, and enabling IPv4 and IPv6 to utilize the same network interface and media, are typically not functions of the MAC sublayer but may be associated with other layers or sublayers within the OSI model.

The two functions performed at the LLC (Logical Link Control) sublayer of the OSI data link layer are:

1. Enables IPv4 and IPv6 to utilize the same network interface and media: The LLC sublayer can support multiple network layer protocols and allows them to share the same network interface and media, facilitating communication for different network protocols.
2. Adds Layer 2 control information to network protocol data: The LLC sublayer is responsible for adding Layer 2 control information, including source and destination MAC addresses, to network protocol data as it prepares data for transmission over the data link layer.

The other options mentioned, such as integrating various physical technologies, implementing a trailer to detect transmission errors, and providing synchronization between source and target nodes, are not typically functions of the LLC sublayer but may be associated with other layers or sublayers within the OSI model.

Here are the two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer:

1. Implements a trailer to detect transmission errors: The MAC sublayer typically appends a frame check sequence (FCS) as part of the trailer to the data frame. This FCS allows the receiver to detect transmission errors and verify the integrity of the received data.
2. Provides synchronization between source and target nodes: The MAC sublayer manages access to the shared communication medium, which involves synchronization to prevent data collisions and ensure efficient data transmission between source and target nodes.

These functions are essential for the proper operation of the MAC sublayer within the data link layer.

Here are the two functions performed at the LLC (Logical Link Control) sublayer of the OSI data link layer:

1. Adds Layer 2 control information to network protocol data: The LLC sublayer is responsible for adding Layer 2 control information, including source and destination MAC addresses, to network protocol data as it prepares data for transmission over the data link layer.
2. Enables IPv4 and IPv6 to utilize the same network interface and media: The LLC sublayer can support multiple network layer protocols and allows them to share the same network interface and media, facilitating communication for different network protocols.

These functions are crucial for the proper operation of the LLC sublayer within the data link layer.

Here are the two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer:

1. Provides synchronization between source and target nodes: The MAC sublayer helps in managing access to the shared communication medium, which involves synchronization to prevent data collisions on shared channels.
2. Integrates various physical technologies: The MAC sublayer is responsible for coordinating and integrating different physical layer technologies, allowing them to work together effectively on the same network.

These functions are essential for the proper operation of the MAC sublayer within the data link layer.

Here are the two functions performed at the LLC (Logical Link Control) sublayer of the OSI data link layer:

1. Adds Layer 2 control information to network protocol data: The LLC sublayer adds Layer 2 control information to the network protocol data as it prepares the data for transmission over the data link layer. This control information includes source and destination MAC addresses, among other information.
2. Places information in the frame that identifies which network layer protocol is being used for the frame: The LLC sublayer includes a field in the data link layer frame that specifies which network layer protocol is being used within the frame. This information allows the receiver to identify and process the network layer protocol encapsulated in the frame.

Here are the two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer:

1. Controls the NIC responsible for sending and receiving data on the physical medium: The MAC sublayer manages the Network Interface Card (NIC) to control the sending and receiving of data frames on the local network segment.
2. Integrates various physical technologies: The MAC sublayer is responsible for integrating and coordinating the use of various physical layer technologies to ensure that data can be transmitted and received effectively over the network. This integration helps in making different network types compatible with each other.

The two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer are:

1. Provides a mechanism to allow multiple devices to communicate over a shared medium: The MAC sublayer is responsible for controlling access to the shared communication medium (e.g., an Ethernet segment) to ensure that multiple devices can transmit and receive data without causing collisions. It implements protocols such as CSMA/CD (Carrier Sense Multiple Access with Collision Detection) or CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).
2. Controls the NIC responsible for sending and receiving data on the physical medium: The MAC sublayer is responsible for managing the Network Interface Card (NIC) to send and receive data frames on the local network segment. It controls how data is placed onto the physical medium, including addressing and frame delimitation.

The other options mentioned are not typically functions of the MAC sublayer. For example, "Places information in the frame that identifies which network layer protocol is being used for the frame" is a function typically associated with the LLC (Logical Link Control) sublayer in the OSI model, and "Communicates between the networking software at the upper layers and the device hardware at the lower layers" describes the role of the entire data link layer, which includes both the LLC and MAC sublayers.

Here are the two functions performed at the LLC (Logical Link Control) sublayer of the OSI data link layer:

1. Enables IPv4 and IPv6 to utilize the same network interface and media: The LLC sublayer helps in multiplexing different network layer protocols, allowing both IPv4 and IPv6 to share the same network interface and media.
2. Places information in the frame that identifies which network layer protocol is being used for the frame: The LLC sublayer includes a field that specifies which network layer protocol is encapsulated within the data link layer frame, enabling the receiver to identify the type of network layer protocol contained in the frame.

Here are the two functions performed at the MAC (Media Access Control) sublayer of the OSI data link layer:

1. Implements a trailer to detect transmission errors: The MAC sublayer typically appends a frame check sequence (FCS) as part of the trailer to the data frame. This FCS allows the receiver to detect transmission errors and verify the integrity of the received data.
2. Controls the NIC responsible for sending and receiving data on the physical medium: The MAC sublayer is responsible for managing access to the physical medium, including controlling the Network Interface Card (NIC) to send and receive data frames on the local network segment.

These functions are essential for reliable and efficient data link layer operation in a network.

The OSI physical layer term that describes the physical medium for microwave transmissions is "air." In the context of microwave communications, data is transmitted through the air using microwave frequencies. This can include wireless communication technologies like microwave links and microwave radio systems. The other terms, such as "goodput," "latency," and "throughput," are related to network performance and data transfer but are not specific to the physical medium used.

The OSI physical layer term that describes the physical medium that uses the propagation of light is "fiber-optic cable." Fiber-optic cables transmit data using the propagation of light signals (optical pulses) through glass or plastic fibers. This technology is known for its high bandwidth, low signal loss, and resistance to electromagnetic interference, making it a popular choice for high-speed data transmission in network communication. The other terms, such as "goodput," "latency," and "throughput," are related to network performance and data transfer but are not specific to the physical medium used.

The OSI physical layer term that describes the physical medium which uses electrical pulses is "copper cable." Copper cables, such as twisted-pair cables (used in Ethernet connections) and coaxial cables, utilize electrical signals in the form of electrical pulses to transmit data. These cables are common for wired network connections and are a physical layer component of network infrastructure.

"Fiber-optic cable" uses light signals (optical pulses) for data transmission, and "air" is not a specific physical medium but is used for wireless communication. "Goodput" refers to the measure of usable data transferred, as explained in a previous response.

The OSI physical layer term that describes the measure of usable data transferred over a given period of time is "goodput." Goodput represents the amount of actual useful data transferred successfully over a network or communication channel, excluding any protocol overhead or retransmissions. It focuses on the data that serves a practical purpose and is typically measured in bits per second (bps) or a similar data rate unit.

The terms "fiber-optic cable," "air," and "copper cable" refer to different physical transmission media, and they are not OSI physical layer terms but are used in the context of the physical layer in networking.

The OSI physical layer term that describes the amount of time, including delays, for data to travel from one point to another is "latency." Latency encompasses the total time delay experienced by data as it travels from its source to its destination, and it includes factors like propagation delay, transmission delay, and processing delay. It is a key factor in determining the performance of a network or communication system.

The other terms, such as "fiber-optic cable," "air," and "copper cable," are not OSI physical layer terms but rather refer to different physical media or transmission mediums used in networking.

The OSI physical layer term that describes the amount of time, including delays, for data to travel from one point to another is "latency." Latency encompasses the total time delay experienced by data as it travels from its source to its destination, and it includes factors like propagation delay, transmission delay, and processing delay. Latency is an important consideration in network performance and can impact the responsiveness of applications and the overall user experience.

The OSI physical layer term that describes the measure of the transfer of bits across a medium over a given period of time is "throughput." Throughput represents the actual data transfer rate achieved in a network or communication channel and takes into account factors such as network congestion, protocol overhead, and any other factors that can affect the efficiency of data transmission. It is typically measured in bits per second (bps) or a similar data rate unit.

The OSI physical layer term that describes the capacity at which a medium can carry data is "bandwidth." Bandwidth refers to the range of frequencies that a communication channel can support and is a measure of the maximum data transfer rate that the channel can handle. It is often expressed in bits per second (bps) or a similar data rate unit. The other terms, throughput, latency, and goodput, are related to network and data transfer performance but represent different aspects of data transmission:

• Throughput: Throughput is the actual data transfer rate achieved in a network or communication channel, which can be less than the available bandwidth due to various factors such as network congestion or protocol overhead.
• Latency: Latency refers to the time delay between the transmission of data and its reception. It includes factors like propagation delay, transmission delay, and processing delay.
• Goodput: Goodput is the measure of the actual useful data transferred over a network or communication channel, excluding overhead and retransmissions. It represents the "good" data delivered successfully.

The OSI physical layer term that describes the capacity at which a medium can carry data is "bandwidth." Bandwidth refers to the range of frequencies that a communication channel can support and is a key factor in determining how much data can be transmitted over that channel. Higher bandwidth channels can carry more data than lower bandwidth channels. The other terms, IEEE and EIA/TIA, are standards organizations, and "air" is not a specific OSI physical layer term.

The OSI physical layer term that describes the process by which one wave modifies another wave is "modulation." Modulation involves varying a carrier signal's properties, such as its amplitude, frequency, or phase, to encode information for transmission over a communication channel. This process allows digital data to be transmitted as analog signals and is a fundamental concept in data transmission and telecommunications. The other terms, IEEE and EIA/TIA, are standards organizations, and "air" is not directly related to the physical layer in the context of OSI model terminology.

Optical fiber cable transmits data over longer distances and at higher bandwidths than any other networking media. Unlike copper wires, fiber-optic cable can transmit signals with less attenuation and is completely immune to EMI and RFI.

Data is transmitted on copper cables as electrical pulses. A detector in the network interface of a destination device must receive a signal that can be successfully decoded to match the signal sent. However, the farther the signal travels, the more it deteriorates. This is referred to as signal attenuation.

Issuing the command i pconfig /all from the PC0 command prompt displays the IPv4 address and MAC address. When the IPv4 address 10.1.1.5 is pinged from PC0, the switch stores the source MAC address (from PC0) along with the port to which PC0 is connected. When the destination reply is received, the switch takes the destination MAC address and compares to MAC addresses stored in the MAC address table. Issuing the show mac-address-table on the PC0 Terminal application displays two dynamic MAC address entries. The MAC address and port entry that does not belong to PC0 must be the MAC address and port of the destination with the IPv4 address 10.1.1.5.

A straight-through cable is commonly used to interconnect a host to a switch and a switch to a router. A crossover cable is used to interconnect similar devices together like switch to a switch, a host to a host, or a router to a router. If a switch has the MDIX capability, a crossover could be used to connect the switch to the router; however, that option is not available. A rollover cable is used to connect to a router or switch console port.

When a cable to an RJ-45 connector is terminated, it is important to ensure that the untwisted wires are not too long and that the flexible plastic sheath surrounding the wires is crimped down and not the bare wires. None of the colored wires should be visible from the bottom of the jack.

Multicast MAC addresses begin with the special value of 01-00-5E.

Cut-through switching provides lower latency switching for high-performance computing (HPC) applications. Cut-through switching allows more invalid frames to cross the network than store-and-forward switching. The cut-through switching method can make a forwarding decision as soon as it looks up the destination MAC address of the frame.

The auto-MDIX feature allows the device to configure its network port according to the cable type that is used (straight-through or crossover) and the type of device that is connected to that port. When a port of a switch is configured with auto-MDIX, this switch can be connected to another switch by the use of either a straight-through cable or a crossover cable.

Logical link control is implemented in software and enables the data link layer to communicate with the upper layers of the protocol suite. Logical link control is specified in the IEEE 802.2 standard. IEEE 802.3 is a suite of standards that define the different Ethernet types. The MAC (Media Access Control) sublayer is responsible for the placement and retrieval of frames on and off the media. The MAC sublayer is also responsible for adding a header and a trailer to the network layer protocol data unit (PDU).

Important actions that a switch performs are as follows:When a frame comes in, the switch examines the Layer 2 source address to build and maintain the Layer 2 MAC address table.
It examines the Layer 2 destination address to determine how to forward the frame. When the destination address is in the MAC address table, then the frame is sent out a particular port. When the address is unknown, the frame is sent to all ports that have devices connected to that network.

When the store-and-forward switching method is used, the switch receives the complete frame before forwarding it on to the destination. The cyclic redundancy check (CRC) part of the trailer is used to determine if the frame has been modified during transit.​​ In contrast, a cut-through switch forwards the frame once the destination Layer 2 address is read. Two types of cut-through switching methods are fast-forward and fragment-free.

The cyclic redundancy check (CRC) part of the trailer is used to determine if the frame has been modified during transit.​ If the integrity of the frame is verified, the frame is forwarded. If the integrity of the frame cannot be verified, then the frame is dropped.

A switch using the store-and-forward switching method performs an error check on an incoming frame by comparing the FCS value against its own FCS calculations after the entire frame is received. In comparison, a switch using the cut-through switching method makes quick forwarding decisions and starts the forwarding process without waiting for the entire frame to be received. Thus a switch using cut-through switching may send invalid frames to the network. The performance of store-and-forward switching is slower compared to cut-through switching performance. Collision detection is monitored by the sending device. Store-and-forward switching does not use IPv4 Layer 3 and 4 information for its forwarding decisions.

Modern switches can negotiate to work in full-duplex mode if both switches are capable. They will negotiate to work using the fastest possible speed and the auto-MDIX feature is enabled by default, so a cable change is not needed.

Fast-forward switching begins to forward a frame after reading the destination MAC address, resulting in the lowest latency. Fragment-free reads the first 64 bytes before forwarding. Store-and-forward has the highest latency because it reads the entire frame before beginning to forward it. Both fragment-free and fast-forward are types of cut-through switching.

The FCS field in a frame is used to detect any errors in the transmission and receipt of a frame. This is done by comparing the CRC value within the frame against a computed CRC value of the frame. If the two values do not match, then the frame is discarded.

Fast-forward and fragment-free switching are variations of cut-through switching, which begins to forward the frame before the entire frame is received.

Store-and forward switching accepts the entire frame and performs error checking using CRC before forwarding the frame. Store-and-forward is often required for QOS analysis. Fast-forward and fragment-free are both variations of the cut-through switching method where only part of the frame is received before the switch begins to forward it.

With shared memory buffering, the number of frames stored in the buffer is restricted only by the of the entire memory buffer and not limited to a single port buffer. This permits larger frames to be transmitted with fewer dropped frames. This is important to asymmetric switching, which applies to this scenario, where frames are being exchanged between ports of different rates. With port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports making it possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. Level 1 cache is memory used in a CPU. Fixed configuration refers to the port arrangement in switch hardware.

The destination MAC address is used for local delivery of Ethernet frames. The MAC (Layer 2) address changes at each network segment along the path. As the frame leaves the web server, it will be delivered by using the MAC address of the default gateway.

The auto-MDIX enables a switch to use a crossover or a straight-through Ethernet cable to connect to a device regardless of the device on the other end of the connection.

Legacy bus-topology Ethernet LAN uses CSMA/CD as network media access control protocol. It works by detecting a collision in the medium and backing off (after transmitting a jam signal) as necessary. When one host wants to transmit a frame, it listens on the medium to check if the medium is busy. After it senses that no one else is transmitting, the host starts transmitting the frame, it also monitors the current level to detect a collision. If it detects a collision, it transmits a special jam signal so that all other hosts can know there was a collision. The other host will receive this jam signal and stop transmitting. After this, both hosts enter an exponential backoff phase and retry transmission.

The data link protocol is responsible for NIC-to-NIC communications within the same network. Although there are many different data link layer protocols that describe data link layer frames, each frame type has three basic parts:
Header
Data
Trailer

Carrier sense multiple access collision detection (CSMA/CD) is the access method used with Ethernet. The access method rule of communication dictates how a network device is able to place a signal on the carrier. CSMA/CD dictates those rules on an Ethernet network and CSMA/CA dictates those rules on an 802.11 wireless LAN.

Layer 2 headers contain the following:Frame start and stop indicator flags at the beginning and end of a frame
Addressing - for Ethernet networks this part of the header contains source and destination MAC addresses
Type field to indicate what Layer 3 protocol is being used
Error detection to determine if the frame arrived without error

When a switch receives a frame with the destination MAC address 01:00:5E:00:00:D9, it typically forwards the frame out all ports except the ingress port. This MAC address falls within a special range used for IPv4 multicast addresses.

Multicast addresses like 01:00:5E:00:00:D9 are used for multicasting IP traffic. By forwarding the frame out all ports except the ingress port, the switch ensures that the multicast frame reaches all devices on the local network segment that have subscribed to that particular multicast group.

This behavior is necessary for multicast communication, as it allows multiple devices to receive the same multicast traffic when they are part of the same multicast group.