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Introduction to Ethernet Switching

CCNA: 0 to Hero - Comprehensive Network Engineering Bootcamp

Lesson 21: Introduction to Ethernet Switching

Layer 2 switches are the backbone of a LAN, connecting end devices and intermediary devices within the same network segment.

Switch Functions

Switches perform three primary functions:

  1. Learning: Building the MAC address table.
  2. Forwarding: Making forwarding decisions based on the MAC address table.
  3. Filtering: Dropping frames that don't need to be forwarded out a specific port.

The MAC Address Table (CAM Table)

Switches maintain a MAC Address Table (Content Addressable Memory - CAM). This table maps MAC addresses to the specific switch port they were learned on.

Learning Process:

When a switch receives a frame, it looks at the Source MAC Address. If the MAC address is not in the CAM table, the switch adds the MAC address and the ingress port to the table.

Default Switch Behavior

By default, a Layer 2 switch operates transparently. All ports are in the same broadcast domain (VLAN 1, by default) and share bandwidth.