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Module 8
Ethernet Switching

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Objectives

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Things to consider…
• Shared Ethernet works very well – within
limits
• What things cause problems that reduce
bandwidth in a shared environment?

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Layer 2 Bridging
• A bridge can be used to create two collision domains
• Source MAC address of a frame and the associated
incoming switch port are added to the address table

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Bridges

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Switch Operation
• Switch – a multiport Bridge
• Divides collision domain into many smaller collision
domains
• Full-Duplex technology

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Full Duplex

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Network Latency

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Spanning-Tree Operation
Multiple paths means that frames can loop

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Switch Modes
• Store and Forward - A switch receives the
entire frame before sending it out the
destination port.
• Cut-Through - A switch starts to transfer the
frame as soon as the destination MAC
address is received.
• Fragment-Free - Read the first 64 octets only
to obtain the header information
–Therefore misses the CRC for checking

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STP States
Spanning Tree Protocol moves from blocking to listening
to learning and then to forwarding or disabled.

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Types of Networks

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Collisions in Collision Domain

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Collision Domain Segmentation

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Increasing a Collision Domain

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Layer 1 Devices Extend Collision Domains

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Limiting the Collision Domains

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Segmenting a Collision Domain with a
Bridge

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Broadcasts in a Bridged Environment

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Effects of Broadcasts in a IP Network

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Broadcast Domain Segmentation

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Data Flow Through a Network with a Router

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Segments

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What is a segment?
From the previous slide the three definitions of a
segment are:
• Term used in the TCP specification to describe a
single transport layer unit of information.
• Section of a network that is bounded by bridges,
routers, or switches.
• In a LAN using a bus topology, a segment is a
continuous electrical circuit that is often
connected to other such segments with repeaters.

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Summary
For more info on switches check out
http://www.bellevuelinux.org/network_switch.html