© 2002, Cisco Systems, Inc. All rights reserved.
Configuring Catalyst Switch Operations
Module 3
Objectives
Upon completing this module, you will be able to:
Explain how bridging and switching operates
Explain the purpose and operations of the Spanning-Tree Protocol
Verify the default configuration of the device, given a functioning access layer switch
Build a functional access switch configuration to support the specified network operational parameters, given a network design
Execute an add, move, or change on an access layer switch, given a new network requirement
© 2002, Cisco Systems, Inc. All rights reserved.
4
Basic Layer 2 Switching and Bridging Functions
Objectives
Upon completing this lesson, you will be able to:
Describe Layer 2 switching and bridging operations and modes
Describe how LAN switches use and populate the MAC address table
Address learning
Forward/filter decision
Loop avoidance
Ethernet Switches and Bridges
Cut-Through
Switch checks destination address and immediately begins forwarding frame.
Fragment-Free
Switch checks the first 64 bytes, then immediately
begins forwarding frame.
Store and Forward
Complete frame is received and checked before forwarding.
Transmitting Frames

MAC Address Table
Initial MAC address table is empty.
Learning Addresses
Station A sends a frame to station C.
Switch caches the MAC address of station A to port E0 by learning the source address of data frames.
The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded).
Learning Addresses (Cont.)
Station D sends a frame to station C.
Switch caches the MAC address of station D to port E3 by learning the source address of data frames.
The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded).
Filtering Frames
Station A sends a frame to station C.
Destination is known; frame is not flooded.
Filtering Frames (Cont.)
Station A sends a frame to station B.
The switch has the address for station B in the MAC address table.
Station D sends a broadcast or multicast frame.
Broadcast and multicast frames are flooded to all ports other than the originating port.
Broadcast and Multicast Frames
Summary
Ethernet switches and bridges increase the available bandwidth of a network by creating dedicated network segments and interconnecting the segments.
Switches and bridges use one of three operating modes to transmit frames: store and forward, cut-through, and fragment-free.
Switches and bridges maintain a MAC address table to store address-to-port mappings so it can determine the locations of connected devices.
When a frame arrives with a known destination address, it is forwarded only on the specific port connected to the destination station.