CISCO NETWORKING ACADEMY PROGRAM (CNAP) SEMESTER 1/ MODULE 8

Ethernet Switching

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CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 6

Ethernet Fundamentals

Objectives

• Upon completion of this module, students will be able to perform tasks related to the following:

• Ethernet Switching • Collision Domains and Broadcast Domains 2

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Layer 2 Bridging • Bridge keeps a table of MAC addresses and the associated ports • The bridge then forwards or discards frames based on the table entries 3

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Layer 2 Switching • Bridge will divide a collision domain but has no effect on a logical or broadcast domain • A switch is essentially a fast, multi-port bridge, which can contain dozens of ports • Rather than creating two collision domains, each port creates its own collision domain • A switch dynamically builds and maintains a Content-Addressable Memory (CAM) table, holding all of the necessary MAC information for each port 4

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Switch Operation • When only one node is connected to a switch port, the collision domain or segment on the shared media contains only two nodes (switch port and host) • These small physical segments are called

microsegments

• Switches are capable of supporting full duplex (capability of communication in both directions at once) • For faster microprocessors and memory, two other technologies made switches possible: • •

Content-addressable memory (CAM)

is memory that allows a switch to directly find the port that is associated with a MAC address without using search algorithms

An application-specific integrated circuit (ASIC)

is a device consisting of logic gates, operations can be done in hardware using an ASIC, reduced the delays caused by software processing 5

Switch Operation

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

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Full Duplex

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

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CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Latency •

Latency

is the delay between the time a frame first starts to leave the source device and the time the first part of the frame reaches its destination • Latency may caused by: • Media delays caused by the finite speed of the physical media • Circuit delays caused by the electronics that process the signal along the path • Software delays caused by the decisions that software must make to implement switching and protocols • Delays caused by the content of the frame and where in the frame switching decisions can be made 8

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Switch Modes • There are 3 switch modes: •

Store and forward

- switch receive the entire frame before sending it out the destination port, Frame Check Sum (FCS) is done to ensure that the frame was reliably received •

Cut-through

- can start to transfer the frame as soon as the destination MAC address is received, no error checking is available •

Fragment-free

- reads the first 64 bytes, which includes the frame header, and switching begins before the entire data field and checksum are read • Store-and-forward mode must be used for asynchronous switching and cut-through must be used in synchronous switching •

Asymmetric

switching provides switched connections between ports of unlike bandwidths, such as a combination of 100 Mbps and 1000 Mbps • S

ymmetric

switching provides each port with same bandwidth 9

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Spanning Tree Protocol • Switched networks are often designed with redundant paths which may leads to switching loop 10

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Spanning Tree Protocol • Spanning-Tree Protocol (STP) is used to solve switching loop by: • Sending Protocol Data Units (BPDUs) out all its ports to let other switches know of its existence and to elect a root bridge for the network.

• Switches then use the Spanning-Tree Algorithm (STA) to resolve and shut down the redundant paths • A port moves through these five states as follows: • From initialization to blocking • From blocking to listening or to disabled • From listening to learning or to disabled • From learning to forwarding or to disabled • From forwarding to disabled 11

Types of Networks

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

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CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Collision Domain • Collision domains are the connected physical network segments where collisions can occur • The types of devices that interconnect the media segments define collision domains: • Layer 1 devices do not break up collision domains • Layer 2 and Layer 3 devices do break up collision domains • Increasing the number of collision domains with Layer 2 and 3 devices is also known as segmentation 13

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Collision Domain • The 5-4-3-2-1 rule requires that the following guidelines should not be exceeded: • • • • •

Five

segments of network media

Four

repeaters or hubs

Three

host segments of the network

Two

link sections (no hosts)

One

large collision domain • Exceeding the four repeater rule, the number of late collisions dramatically increases 14

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Segmentation • Layer 2 devices segment or divide collision domains by using MAC addresses to make forwarding decision • By using bridges and switches, the collision domain is broken up into smaller parts, each becoming its own collision domain. • Layer 3 devices, like Layer 2 devices, do not forward collisions.

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CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Layer 2 Broadcasts • To communicate with all collision domains, protocols use broadcast and multicast frames at Layer 2 of the OSI model. • When a node needs to communicate with all hosts on the network, it sends a broadcast frame with a destination MAC address 0xFFFFFFFFFFFF like Address Resolution Protocol (ARP) • Source of broadcasting are workstations, routers and multicast applications • The circulation of broadcast radiation can saturate the network so that there is no bandwidth left for application data, this situation known as a

broadcast storm

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CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Broadcast Domains • A broadcast domain is a grouping of collision domains that are connected by Layer 2 devices •

Broadcast domains are controlled or segmented at Layer 3

because routers do not forward broadcasts • Because routers forward packet based on IP address, not MAC address 17

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

Introduction to Data Flow • Layer 1 devices do no filtering, so everything that is received is passed on to the next segment • Layer 2 devices filter data frames based on the destination MAC address • Layer 3 devices filter data packets based on IP destination address 18

What is network segment?

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

Ethernet Switching

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Summary

CISCO NETWORKING ACADEMY PROGRAM SEMESTER 1/ MODULE 8

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