Ethernet Switching - Module 7: Introduction to Networks (Cisco Netacad)

Overview

• Module 7 focuses on Ethernet switching in networks.
• Topics include Ethernet frames, MAC address table, switch speeds, and forwarding methods.

Ethernet Frames

• Ethernet operates at Data Link and Physical layers.
• Defined by IEEE 802.2 (LLC) and IEEE 802.3 (MAC and Physical layers).
• Data Link Layer divided into:
  • LLC Sub-layer: Identifies network layer protocol.
  • MAC Sub-layer: Data encapsulation, media access, addressing.

Frame Fields

• Fields: Preamble, Start Frame Delimiter, Destination MAC Address, Source MAC Address, Type/Length, Data (Payload), Frame Check Sequence (FCS).
• Frame size: Minimum 64 bytes, maximum 1518 bytes (excluding preamble).
• Frames larger than 1500 bytes are jumbo frames and typically supported.
• FCS used for error detection.

Ethernet MAC Addresses

• Layer 2 addresses or MAC addresses used for local delivery within a LAN.
• MAC address changes at each hop, but IP addresses remain unchanged.

Structure

• 48-bit binary value, expressed as 12 hexadecimal values.
• Consists of two parts:
  • OUI (Organizationally Unique Identifier) assigned by IEEE.
  • Device-specific value assigned by manufacturer.

Frame Processing

• Source and destination MAC addresses included in Ethernet frame headers.
• Unicast, Broadcast, and Multicast addressed frames processed differently.
  • Unicast: From single transmitter to single receiver.
  • Broadcast: Sent to all devices in the network.
  • Multicast: Sent to a group of devices.

MAC Address Table

• Layer 2 switches use MAC addresses for forwarding decisions.
• MAC Address Table (or CAM Table) stores MAC addresses and corresponding ports.
• Switch learns MAC addresses dynamically by examining source addresses.

Learning and Forwarding

• Examines source MAC to learn, checks destination MAC to forward.
• If destination MAC is unknown, switch floods frame to all ports except incoming.

Switch Speeds and Forwarding Methods

• Forwarding Methods:
  • Store-and-Forward: Stores entire frame, checks for errors, then forwards.
  • Cut-Through: Forwards frame after reading destination address.
    • Variants: Fast Forward and Fragment Free.

Memory Buffering on Switches

• Port-based memory: Linked to specific ports, can cause delays.
• Shared memory: Common buffer for all ports, more efficient handling.

Duplex and Speed Settings

• Duplex Settings:
  • Full Duplex: Simultaneous send/receive.
  • Half Duplex: Send and receive alternately.
• Auto-negotiation helps configure optimal settings.

Issues

• Duplex mismatch can cause performance issues.
• Auto-MDIX feature can automatically configure cable types.

Conclusion

• Ethernet involves complex processes at various OSI layers.
• Understanding MAC addressing and switch operations is crucial for network engineering.
• Practice with labs and exercises to reinforce learning.