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Switches are network devices that forward frames across a common shared communications media such as copper wires or fiber optic cable. Switches are advanced, multiport bridges that learn all the physical addresses (MAC addresses) of devices attached to the switch and cross reference that list of physical addresses with the physical ports those the devices with those addresses are plugged in to. This table of MAC addresses and ports (sometimes called a MAC or ARP table) allows a switch to forward frames to the correct device without broadcasting an ARP packet to learn a physical address. Switches segment collision domains into an individual links between the switch and a directly attached end station.

Because each device is attached directly to the switch across a full-duplex path, there are no collisions and the device operates at nearly the full data rate of the connected network interface. Note that switches do not reduce logical (network layer) broadcast domains.

SWITCHING CONCEPTS

• Collision Domain
• Broadcast Domain
• Spanning Tree (from bridging section)

SWITCH ARCHITECTURES

• Crossbar vs. Hierarchical
• Store and forward vs. Cut-Through

Books on Switching

Interconnections (2nd Ed.) - Radia Perlman Radia Perlman's definitive work on switching. Great book for those tricky questions on certification exams having to do with operation and behavior, rather than configuration commands. General, not specific to any vendor, which is why it is so good. Anything you learn here will work everywhere.
Cisco LAN Switching Fundamentals Barnes, Sakandar A good mix of theory and practical configuration advice. Again, comes from a Cisco perspective, and covers Cisco proprietary functionality.
Cisco Lan Switching Configuration Handbook - McQuerry, Jansen Hucaby Good book on configuring Cisco switching gear. Clear, to the point. Helps with the general questions on certification exams pertaining to specific configuration commands.
JUNOS Enterprise Switching Reynolds, Marchke Prepares the reader for the JNTCP (Juniper Network Technical Certification Program) switching exam and useful for when you're working on Juniper EX switches.