Ethernet Switching and LAN Technologies

Fragment-Free Switching

• A compromise between store-and-forward and fast-forward switching methods, ensuring low latency and high integrity.
• The switch stores and performs error checks on the first 64 bytes of the frame before forwarding.

Switch Speeds and Forwarding Methods

• Memory Buffering:
  • Frames are stored in queues linked to specific incoming and outgoing ports.
  • Frames are transmitted to the outgoing port only when all frames ahead in the queue have been successfully transmitted.
  • A single frame can delay the transmission of all frames in memory due to a busy destination port.
• 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.
  • Frames are dynamically linked to the destination port, enabling packet transmission without moving to a different queue.

Ethernet MAC Addresses

• Unicast MAC Address:
  • A unique address used when a frame is sent from a single transmitting device to a single destination device.
  • The source MAC address must always be a unicast.
  • ARP (Address Resolution Protocol) is used to determine the destination MAC address associated with an IPv4 address.
  • Neighbor Discovery (ND) is used to determine the destination MAC address associated with an IPv6 address.
• Broadcast MAC Address:
  • Received and processed by every device on the Ethernet LAN.
  • Has a destination MAC address of FF-FF-FF-FF-FF-FF in hexadecimal.
  • Flooded out all Ethernet switch ports except the incoming port.
  • Not forwarded by a router.
• Multicast MAC Address:
  • Received and processed by a group of devices that belong to the same multicast group.
  • Destination MAC address of 01-00-5E for IPv4 multicast packets and 33-33 for IPv6 multicast packets.
  • Flooded out all Ethernet switch ports except the incoming port, unless the switch is configured for multicast snooping.
  • Not forwarded by a router, unless the router is configured to route multicast packets.

LAN Technologies

• Ethernet:
  • Uses wired communications, including twisted-pair, fiber-optic links, and coaxial cables.
  • Supports bandwidths of up to 100 Gbps.
• Wireless LANs (WLANs):
  • A network that wirelessly connects users and devices in a small geographic area.
  • Uses radio waves to transmit data between wireless devices.

Ethernet Frames

• Ethernet operates in the data link layer and the physical layer.
• Defined in the IEEE 802.2 and 802.3 standards.
• Data Link Sublayers:
  • LLC Sublayer (IEEE 802.2):
    • Communicates between the networking software and device hardware.
    • Places information in the frame to identify which network layer protocol is used.
  • MAC Sublayer (IEEE 802.3, 802.11, and 802.15):
    • Responsible for data encapsulation and media access control.
    • Implemented in hardware.

Switch Fundamentals

• A Layer 2 Ethernet switch uses Layer 2 MAC addresses to make forwarding decisions.
• Unaware of the data being carried in the frame, such as IPv4, ARP, or IPv6 packets.
• Discards frames with errors, reducing bandwidth consumed by corrupt data.
• Store-and-forward switching is required for QoS analysis on converged networks.

Learn about the two most prominent LAN technologies, Ethernet and Wireless LANs (WLANs), and their characteristics. Understand the features and advantages of each technology.