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
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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
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
Layer 2 Switching
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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
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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
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
Switch Operation
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
Full Duplex
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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
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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
• Symmetric switching provides each port with same bandwidth
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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
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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
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
Types of Networks
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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
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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
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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
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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
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
What is network segment?
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CISCO NETWORKING ACADEMY PROGRAM
SEMESTER 1/ MODULE 8
Ethernet Switching
Summary
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