Transcript
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 1/70
CCNA version 3
Module 4
Switching Concepts
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 2/70
CCNA version 3
Summary
LAN congestion and its effect onnetwork performance
Advantages of LAN segmentation in a
network Advantages and disadvantages of
using bridges, switches, and routers
for LAN segmentation Effects of switching, bridging, androuting on network throughput FastEthernet technology and its benefits
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 3/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 4/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 5/70
CCNA version 3
CSMA/CD prevents multiple devices from
transmitting at the same time.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 6/70
CCNA version 3
The Ethernet/802.3
Interface Ethernet is known as a shared-
medium technology ² all the devicesare connected to the same deliverymedia.
Ethernet media uses a data frame
broadcast method of transmittingand receiving data to all nodes on theshared media.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 7/70
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 8/70
CCNA version 3
Performance of a shared mediaEthernet/802.3 LAN can benegatively effected by severalfactors.
y The data frame broadcast delivery nature of
Ethernet/802.3 LANsy CSMA/CD access methods allow only one station
to transmit at a time.
y Network congestion due to increased bandwidthdemands from multimedia applications such as
video and the Internet.y Normal latency (propagation delay) of frames as
they travel across the LAN layer 1 media and passthrough layer 1, 2 and 3 networking devices.
y Extending the distances of the Ethernet/802.3
LANs using Layer 1 repeaters.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 9/70
CCNA version 3
Half-Duplex Design
Loopback
TxTx
RxRx
Collision
Detection
Ethernet
Controller
TxTx
RxRx
Collision
Detection
Ethernet
Controller
Transmit
Receive
Loopback
Ethernet NIC Ethernet NIC
Ethernet physical connector provides several circuits
Most important are receive (RX), transmit (TX), andcollision detection
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 10/70
CCNA version 3
Half-Duplex Ethernet
Design (Standard Ethernet) The most important of these circuits
are the receive (RX), transmit (TX)and collision detection.
The transmit (TX) circuit is active atthe transmitting station.
The receive (RX) circuit is active atthe receiving station.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 11/70
CCNA version 3
To the network this appears as a single one
way bridge. Both devices are contending for the rightto use the single shared medium.
The collision detection circuit on each
node contends for the use of the networkwhen the two nodes attempt to transmit atthe same time.
When a collision occurs, a host will first
listen to see if the network is in usebefore trying to retransmit. It willresume transmitting based on the back-off algorithm.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 12/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 13/70
CCNA version 3
Congestion and Bandwidth To relieve network congestion more
bandwidth is needed or the availablebandwidth must be used more
efficiently. ´Throwing bandwidth at the problem.µ
Attacking the symptom and not
always the problem (illness), i.e. Couldbe broadcasts, chatty protocols,applications traffic, etc.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 14/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 15/70
CCNA version 3
Propagation Delay
Latency is also known as propagation delay.
Propagation delay is the time a frame orpacket of data takes to travel from thesource station or node to its finaldestination on the network.
The greater the number of devices the
greater the latency or propagation delay adding hosts simply increases collisions,
increases jam signals, and throughput willdecrease
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 16/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 17/70
CCNA version 3
Ethernet Transmission
Times Each Ethernet bit has a 100ns
window for transmission.
A byte is equal to eight bits.
Therefore, one byte takes a minimumof 800ns to transmit (8 bits at 100nsper equals 800ns).
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 18/70
CCNA version 3
A 64 byte frame takes 51,200ns or
51.2 microseconds to transmit (64bytes at 800ns equals 51,200ns,51,200ns/1000 equals 51.2microseconds).
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 19/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 20/70
CCNA version 3
Extending Shared Media
LANs using Repeaters Signal attenuation ² the signal
weakens as it travels through thenetwork from the resistance found inthe medium.
An Ethernet repeater to extend the
distance of a LAN is that a singlenetwork can cover a greater distanceand more users can share that same
network. (Coverage Area)
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 21/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 22/70
CCNA version 3
Improving LANPerformance
The performance of a network can beimproved in a shared media LAN such
as Ethernet by using one or more ofthe following solutions:
y Segmenting the network using Bridges,Routers, or LAN Switches
y Move to full duplex transmitting
y Upgrade to the Fast Ethernet Standard
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 23/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 24/70
CCNA version 3
Why Segment LANs?
A Cisco Segment A network can be divided in smaller
units called segments. Each segment
uses the (CSMA/CD) protocol andmaintains traffic between users onthe segment. By using segments in anetwork less users/devices are
sharing the same 10Mbps whencommunicating to one another withinthe segment. Each segment is
considered its own collision domain.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 25/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 26/70
CCNA version 3
Why Segment LANs? In a segmented Ethernet LAN data
passed between segments is
transmitted on the backbone of thenetwork using a bridge, switch, orrouter.
The backbone network is its owncollision domain and uses CSMA/CD toprovide a best effort delivery service
between segments.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 27/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 28/70
CCNA version 3
Segmentation with Bridges
Bridges are different than routersbecause they are Layer 2 devices,independent of Layer 3 protocols ²
they pass on data frames regardlessof which Layer 3 protocol is beingused and are transparent to theother devices on the network.
Bridges increase the latency (delay)ina network by 10-30%.
Why?
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 29/70
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 30/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 31/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 32/70
CCNA version 3
Segmentation with Routers Routers operate at the network layer
and base all of their forwarding
decisions between segments on theLayer 3 protocol address.
Because routers perform more
functions than bridges they operatewith a higher rate of latency.(Higher than other internetworkingdevices.)
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 33/70
CCNA version 3
Routers: Segment broadcast domains
Forward packets based on destinationnetwork layer addresses
Segment collision domains
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 34/70
CCNA version 3
More collision domains,but more bandwidthfor each user
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 35/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 36/70
CCNA version 3
Segmentation with LAN
Switches A switch segments a LAN into
microsegments creating collision free
domains from one larger collisiondomain, not broadcast domains.
With switched ethernet
implementation the availablebandwidth can reach closer to 100%.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 37/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 38/70
CCNA version 3
LAN Switch Latency Each switch used on an Ethernet LAN
adds latency to the network.
However, the type of switching usedcan help overcome the built in latencyof some switches.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 39/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 40/70
CCNA version 3
Full-Duplex Ethernet
Overview Full duplex Ethernet allows the
transmission of a packet and the
reception of a different packet atthe same time.
Requires two pairs of conductors
and a switched connection betweeneach node
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 41/70
CCNA version 3
Simultaneous transmission and
reception of frames is calledbidirectional traffic (both directions)and yields 20Mbps of throughput.
The network interface cards (NICs)on both ends need to have full duplexcapabilities.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 42/70
CCNA version 3
Full-Duplex Ethernet Design
Transmit circuit connects directly to receive circuit
No collisions Significant performance improvement
Eliminates contention on Ethernet point-to-point link
Uses a single port for each full-duplexconnection
TX
Full
Duplex
Ethernet
Controller
Loopback
TxTx
RxRx
Collision
DetectionRX
Full
Duplex
Ethernet
Controller
Loopback
TxTx
RxRx
Collision
Detection
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 43/70
CCNA version 3
Using Full Duplex
Node must
² Be directly attached to a dedicatedswitched port
² Have installed network interface card thatsupportsfull duplex
Full Duplex
Half Duplex
HUB
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 44/70
CCNA version 3
Full-Duplex Ethernet
Design Standard Ethernet normally can onlyuse 50-60% of the 10Mbps availablebandwidth.
This is due to collisions and latency.
Full duplex Ethernet offers 100% ofthe bandwidth in both directions.
This produces a potential 20Mbpsthroughput ² 10Mbps TX and 10MbpsRX.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 45/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 46/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 47/70
CCNA version 3
This virtual network circuit exists
only when two nodes need tocommunicate.
This is why it is called a virtual circuit
² it exists only when needed and isestablished within the switch.
Allows multiple users to communicatein parallel via these virtual circuits.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 48/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 49/70
CCNA version 3
Source MACaddress is used
to build thistable
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 50/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 51/70
CCNA version 3
How a LAN Switch Learns
Addresses This means that as new addresses are
read they are learned and stored in
Content Address Memory (CAM). Each time an address is stored it is
time stamped.
This allows addresses to be storedfor a set period of time.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 52/70
CCNA version 3
But more domains
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 53/70
CCNA version 3
Benefits of Switching A LAN switch allows many users to
communicate in parallel through the
use of virtual circuits and dedicatednetwork segments in a collision freeenvironment.
Cost effective.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 54/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 55/70
CCNA version 3
Symmetric Switching A symmetric switch is optimized
through even distribution of network
traffic across the entire network .
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 56/70
CCNA version 3
before forwarding
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 57/70
CCNA version 3
Asymmetric Switching Asymmetric switching is optimized
for client-server network traffic
flows where multiple clients aresimultaneously communicating with aserver, requiring more bandwidth
dedicated to the switch port that theserver is connected to in order toprevent a bottleneck at that port.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 58/70
CCNA version 3
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 59/70
CCNA version 3
Memory Buffering The area of memory where the switch
stores the destination and
transmission data is called thememory buffer.
This memory buffer can make use of
two methods for forwarding packets² port based memory buffering orshared memory buffering.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 60/70
CCNA version 3
Port based memory buffering
packets are stored in queues that arelinked to specific incoming ports.
² Problem: One port may fill while anotheris empty.
Shared memory buffering depositsall packets into a common memorybuffer that is shared by all the ports
on the switch. (Better!)
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 61/70
CCNA version 3
3 frame transmission modes
in a switch (+ 1 variation)
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 62/70
CCNA version 3
Three Switching Methods
Store and Forward - the entireframe is received before anyforwarding takes place.
Latency occurs while the frame isbeing received; the latency is greaterwith larger frames because the entireframe takes longer to read.
Error detection is high because ofthe time available to the switch tocheck for errors while waiting for the
entire frame to be received.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 63/70
CCNA version 3
Cut-through the switch reads the
destination address before receivingthe entire frame.
The frame is then forwarded before
the entire frame arrives. This mode decreases the latency of
the transmission and has poor error
detection.
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 64/70
CCNA version 3
Fragment-Free Switching
Switch reads the 1st 64bytes of the incomingframe beforeforwarding it to the
destination port
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 65/70
CCNA version 3
Means theswitch is in cutthrough mode
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 66/70
CCNA version 3
Adaptive Cut Through
Combines cut through and store andforward
The switch uses cut-through untilthere are a given number of errors
Then the switch will change to store
and forward method
Emerging Trends:
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 67/70
CCNA version 3
Emerging Trends:The Network Evolution
Shared to Switched
The
New
Wiring
Closet
VLAN
System
LAN
Campus
Switch
The New Backbone
The
Old
Wiring
Closet
HUB
HUB
HUB
HUB
HUB
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 68/70
CCNA version 3
Benefits of Switching
Number of collisions reduced
Simultaneous, multiple communications
High-speed uplinks
Improved network response
Increased user productivity
8/3/2019 Ccna 3mod4 Switching Concepts
http://slidepdf.com/reader/full/ccna-3mod4-switching-concepts 69/70
CCNA version 3
Switching? Routing?
What·s the difference? In a switching network, you'll find the
intermediate devices keeping track of - or
remembering - qualities of the connection. In a pure routing network, the
intermediate devices will be indifferent toanything but handing off packets to the
next device, and they will not be distractedby any other information, upstream ordownstream.
top related