Networking: Switch Operations and Methods

Forward/Filter Decisions

• Switch identifies the exit interface using the destination MAC address found in the MAC address table.
• Frames are forwarded only through the specified destination port.

Loop Avoidance

• Redundant connections between switches may lead to network loops.
• Spanning Tree Protocol (STP) effectively prevents loops while allowing redundancy in the network.

Switch Internal Processing

• Switches process frames to ensure efficient data forwarding through various methods.

Frame Forwarding Methods

• Store-and-Forward Switching

  • Entire frame is received before forwarding.
  • Switch verifies frame integrity by comparing frame-check-sequence (FCS) values.
  • Only error-free frames are forwarded, enhancing reliability.

• Cut-Through Switching

  • Switch forwards frames immediately after determining the destination MAC address.
  • Potentially forwards frames with errors, prioritizing speed over error-checking.

• Fragment Free Switching

  • A variation of cut-through switching that waits for the collision window (64 bytes) to pass.
  • Better error checking than cut-through with minimal increase in latency.

Switch Types

• Layer 2 Switch: Operates at Data Link layer, managing local traffic.
• Layer 3 Switch: Operates at Network layer, can route packets.

Switch Form Factors

• Fixed Configuration: Pre-defined ports and features.
• Modular Configuration: Expandable with additional hardware modules.
• Stackable Configuration: Several units can be stacked and managed as a single device.

Business Considerations for Switch Selection

• Cost: Assess initial investment and long-term value.
• Speed and Interfaces: Evaluate required bandwidth and port quantity.
• Expansion Capability: Consider future network growth.
• Port Density: Justify the number of devices on the network.
• Power: Look into options for Power over Ethernet (PoE) and backup power supplies.
• Reliability: Ensure switches provide continuous access.
• Port Speed: Choose between Ethernet, FastEthernet, GigabitEthernet based on requirements.
• Scalability: Anticipate network expansion needs.

Switch Functions

• Address Learning: Switches store source MAC addresses from incoming frames into the MAC address table.
• Forward/Filter Decisions: Based on the MAC address table, switches manage frame delivery.
• Loop Avoidance: Mechanisms like STP are employed to manage potential network loops.

MAC Address Table

• Switches construct a MAC address table that tracks the devices connected to each port.
• This table is pivotal for determining how frames are processed and directed within the network.

Address Learning Process

• Layer 2 switches and bridges accumulate source MAC addresses from received frames.
• These addresses are entered into a MAC address table, forming the basis for future forwarding decisions.

This quiz focuses on the operations of network switches, including frame forwarding methods like Store-and-Forward and Cut-Through Switching. Additionally, it covers loop avoidance strategies such as the Spanning Tree Protocol (STP) and the process behind how switches handle data. Test your knowledge on the internal workings and decision-making processes of switches.