Ethernet Switching Overview
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Ethernet Switching Overview

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Questions and Answers

Which of the following methods can be used to learn routes that the router does not have a direct connection to?

  • Manually and Dynamically (correct)
  • Automatically and Preset
  • Dynamically and Automatically
  • Manually and Communicatively

    • What does a default route do when routing traffic?

  • Forwards all traffic to a specified direction when no match is found (correct)
  • Routes all traffic to the local interface
  • Automatically routes traffic based on the highest priority path
  • Denies all traffic not explicitly defined

    • What is the primary function of dynamic routing protocols?

  • To share routing information among routers (correct)
  • To configure static routes manually
  • To establish a direct connection to remote networks
  • To prevent network topology changes

    • Which command can be used to display the types of routing sources and their statuses?

    <p>show ip route</p> Signup and view all the answers

    What does a static route represent in routing terminology?

    <p>A route configured manually by an administrator</p> Signup and view all the answers

    What layers of the OSI model does Ethernet operate in?

    <p>Data link and Physical layers</p> Signup and view all the answers

    What does the LLC sublayer provide that differentiates it from the MAC sublayer?

    <p>Identification of the network layer protocol</p> Signup and view all the answers

    Which term refers to the error detection mechanism included in the Ethernet frame?

    <p>Frame Check Sequence</p> Signup and view all the answers

    In terms of Ethernet communications, what is the primary function of the MAC sublayer?

    <p>Handling data encapsulation and media access control</p> Signup and view all the answers

    What happens to Ethernet frames that are less than 64 bytes in length?

    <p>They are considered collision fragments and discarded</p> Signup and view all the answers

    What is required when using full-duplex Ethernet communications?

    <p>No access control through CSMA/CD</p> Signup and view all the answers

    What is the maximum size of an Ethernet frame?

    <p>1518 bytes</p> Signup and view all the answers

    What term describes frames that exceed 1500 bytes in size?

    <p>Jumbo frames</p> Signup and view all the answers

    What is the total number of bits in an Ethernet MAC address?

    <p>48 bits</p> Signup and view all the answers

    Which of the following hexadecimal values represents the binary number 0000 1010?

    <p>0x0A</p> Signup and view all the answers

    What does the acronym OUI refer to in the context of Ethernet MAC addresses?

    <p>Organizationally Unique Identifier</p> Signup and view all the answers

    What data link layer addressing method is utilized in Ethernet networks for device identification?

    <p>MAC Addressing</p> Signup and view all the answers

    Which two components are included in an Ethernet frame that a NIC uses when forwarding messages?

    <p>Source MAC and Destination MAC</p> Signup and view all the answers

    What is the hexadecimal value range that can be represented with a byte?

    <p>00 to FF</p> Signup and view all the answers

    How many hexadecimal digits represent an Ethernet MAC address?

    <p>12</p> Signup and view all the answers

    What type of address does an Ethernet switch use to make forwarding decisions?

    <p>Layer 2 Ethernet MAC addresses</p> Signup and view all the answers

    What happens when a NIC receives an Ethernet frame with a MAC address that does not match its own?

    <p>It discards the frame.</p> Signup and view all the answers

    What happens to a MAC address that does not exist in the switch's MAC address table?

    <p>It is added to the table with the incoming port number.</p> Signup and view all the answers

    For how long does a switch retain an entry in its MAC address table by default?

    <p>5 minutes</p> Signup and view all the answers

    What type of address is treated as a new entry if it appears on a different port?

    <p>Source MAC address</p> Signup and view all the answers

    What is the action taken if the destination MAC address is not found in the MAC address table?

    <p>The switch forwards the frame out all ports except the incoming port.</p> Signup and view all the answers

    Which option best describes what Content Addressable Memory (CAM) is used for in an Ethernet switch?

    <p>Storing MAC addresses</p> Signup and view all the answers

    What does the switch do to refresh the timer for a MAC address in its table?

    <p>It updates the entry with a new port but the same MAC address.</p> Signup and view all the answers

    What happens when a switch receives a frame with a broadcast MAC address?

    <p>The switch floods it out all ports except the incoming port.</p> Signup and view all the answers

    What does full-duplex communication allow for in a network connection?

    <p>Devices can send and receive data simultaneously.</p> Signup and view all the answers

    What commonly causes performance issues on 10/100 Mbps Ethernet links?

    <p>Duplex mismatch</p> Signup and view all the answers

    Which statement about half-duplex communication is true?

    <p>Only one end can transmit data at a time.</p> Signup and view all the answers

    What is the role of autonegotiation in networking?

    <p>Negotiating speed and duplex capabilities between devices.</p> Signup and view all the answers

    What condition leads to a duplex mismatch?

    <p>One end operates in half-duplex while the other operates in full-duplex.</p> Signup and view all the answers

    Which of the following is true about the auto-MDIX feature?

    <p>It is enabled by default on Cisco IOS Release 12.2(18)SE or later.</p> Signup and view all the answers

    What is the recommended best practice regarding duplex configuration on Ethernet switch ports?

    <p>Both ports should be configured as full-duplex.</p> Signup and view all the answers

    Which of the following protocols is utilized at the network layer?

    <p>IP version 4 (IPv4)</p> Signup and view all the answers

    Study Notes

    Ethernet Switching

    • Operates in data link and physical layers.
    • Defined by the IEEE 802.2 and 802.3 standards.
    • LLC and MAC are two sublayers of the data link layer.
    • LLC (Logical Link Control) places information in the frame to identify the network layer protocol being used.
    • MAC (Media Access Control) handles data encapsulation, media access control, and provides data link layer addressing.
    • Data Encapsulation includes:
      • Ethernet frame: internal structure of the frame.
      • Ethernet Addressing: uses source and destination MAC addresses to deliver frames between NICs on the same LAN.
      • Ethernet Error Detection: uses a frame check sequence (FCS) trailer.
    • The MAC sublayer defines specifications for Ethernet communication standards over various media (copper, fiber).
    • Legacy Ethernet uses a shared, half-duplex medium with a bus topology or hubs.
    • Half-duplex communication uses CSMA/CD (Carrier Sense Multiple Access/Collision Detection).
    • Modern Ethernet LANs use switches that operate in full-duplex.
    • Full-duplex communication does not require CSMA/CD for access control.
    • The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes. The preamble field is not included in the frame size.
    • Frames less than 64 bytes are considered collision fragments and are discarded.
    • Frames larger than 1500 bytes are considered jumbo or baby giant frames.
    • If the size of a transmitted frame is outside the limits, the receiving device drops the frame.
    • Dropped frames are likely caused by collisions or unwanted signals and are considered invalid.
    • Jumbo frames are often supported by Fast Ethernet and Gigabit Ethernet switches and NICs.
    • An Ethernet MAC address is a 48-bit binary value, expressed using 12 hexadecimal values (00 to FF).
    • Leading zeroes are always displayed in hexadecimal representation to complete the 8-bit representation.
    • Hexadecimal values are often represented with a '0x' prefix (e.g., 0x73) or a subscript '16' (e.g., 73_16) or an 'H' suffix (e.g., 73H).

    MAC Addressing

    • All network devices on an Ethernet LAN are connected to the same, shared media.
    • MAC addressing identifies devices at the data link layer.
    • An Ethernet MAC address is a 48-bit address consisting of 12 hexadecimal digits (6 bytes in length).
    • All MAC addresses must be unique.
    • Vendors selling Ethernet devices must register with the IEEE to obtain a unique 6 hexadecimal (24-bit) code called an OUI (Organizationally Unique Identifier).
    • An Ethernet MAC address consists of a 6 hexadecimal vendor code followed by a 6 hexadecimal NIC-assigned value.

    Switch Operation

    • When forwarding a message, an Ethernet NIC includes a Source MAC address and a Destination MAC address.
    • When receiving a frame, an NIC checks the Destination MAC address against its own physical MAC address. If a match is found, the frame is passed to higher OSI layers. If there is no match, the frame is discarded.
    • NICs accept frames with unicast or multicast destination MAC addresses if the host is a member of that group.
    • Every network device with an Ethernet NIC has a MAC address.
    • Switches make forwarding decisions based solely on the Layer 2 Ethernet MAC addresses.
    • When a switch is turned on, its MAC address table is empty.
    • Switches use Content Addressable Memory (CAM) to store MAC address table entries.
    • Each frame entering a switch is checked for new information. The Source MAC address and port number are used to create or update the MAC address table.
    • Entries in the MAC address table are typically kept for 5 minutes.
    • If a Source MAC address is found in the table but on a different port, it is treated as a new entry. The entry is replaced with the most current port number.
    • If the Destination MAC address is a unicast address, the switch looks for a match in its MAC address table. If found, the frame is forwarded out the specified port. Otherwise, the frame is flooded out all ports except the incoming port (unknown unicast).
    • Broadcast and multicast frames are flooded out all ports except the incoming port.

    Duplex Modes

    • Full-duplex: both ends of the connection can send and receive simultaneously.
    • Half-duplex: only one end of the connection can send at a time.

    Autonegotiation

    • Autonegotiation is an optional function on Ethernet switches and NICs. It allows devices to automatically negotiate the best speed and duplex capabilities.
    • Gigabit Ethernet ports operate in full-duplex only.

    Duplex Mismatch

    • Duplex mismatch is a common cause of performance issues on 10/100 Mbps Ethernet links.
    • It occurs when one port on the link operates in half-duplex and the other operates in full-duplex.
    • This can occur when ports are reset and autonegotiation does not result in consistent configurations.
    • Best Practice: Configure both Ethernet switch ports to full-duplex.

    Auto-MDIX (Automatic Medium-Dependent Interface Crossover)

    • Most switches support auto-MDIX.
    • It automatically detects the type of cable connected to the port and configures the interfaces accordingly.
    • Auto-MDIX is enabled by default on switches running Cisco IOS Release 12.2(18)SE or later but can be disabled.
    • Best Practice: Use the correct cable type and do not rely on auto-MDIX.
    • The 'mdix auto' command can re-enable auto-MDIX.

    Network Layer

    • The Network Layer provides services for end devices to exchange data.

    • Primary Network Layer communication protocols are IP version 4 (IPv4) and IP version 6 (IPv6).

    • The four basic operations of the network Layer are:

      • Addressing
      • Routing
      • Packet forwarding
      • Fragmentation

    • Routers provide services for packet forwarding and fragmentation.

    • Routing is the process of determining the path that data will travel between source and destination networks.

    • Routes that routers do not have a direct connection to can be learned either manually or dynamically.

    • Manually configuring routes is done with static routes.

    • Dynamically learning routes utilizes routing protocols to share information between routers.

    • A default route forwards all traffic to a specific direction if a matching route is not found in the routing table.

    • Default routes must be configured manually.

    • Dynamic routing automatically discovers remote networks, maintains updated information, chooses the best path, and finds new paths when the topology changes.

    • show ip route command displays route sources and types:

      • L: directly connected local interface IP address.
      • C: directly connected network.
      • S: static route configured manually.
      • O: OSPF
      • D: EIGRP

    • Directly Connected routes: C and L

    • **Remote Routes: ** O, D, etc

    • Default Routes: S

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    Description

    Explore the fundamental concepts of Ethernet switching in this quiz, focusing on its operations within the data link and physical layers. Understand the key components such as LLC and MAC sublayers, data encapsulation, and error detection methods. Test your knowledge on Ethernet standards and communication techniques.

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