CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Switching Concepts
Introduction to Ethernet/802.3 LANsIntroduction to LAN Switching
Switch Operation
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Switching Concepts
Introduction to Ethernet/802.3 LANs
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Ethernet Technology Overview• Ethernet multi-access
broadcast technology• Uses CSMA/CD• Collisions impact on
network performance• Layer 2 devices can
improve performance• Media includes CAT5(e),
fibre, wireless • Speeds from 10Mbps to
10,000 Mbps
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Network Growth• Bandwidth needs have increased
– Internet/intranet/email– Multimedia– Increasing use of enterprise servers
• Ethernet has developed to meet challenge– 10Mbps, 100Mbps, 1000Mbps, 10Gbit– Coaxial, Twisted Pair, Fibre Optic, Wireless– Repeaters, hubs, bridges, switches, routers
• BUT you must understand the features of all this technology to gain best performance in your network design!
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Hubs• Layer 1 devices• Regenerate, retime,
amplify signals• 1 collision/bandwidth
domain• Broadcasts propagated
out of every port• Only 1 device can
transmit at a time• Only 50-60% bandwidth
available
thick Ethernet or thin Ethernet infrastructures
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Bridges• Layer 2 device• Splits network into 2
collision/bandwidth domains
• Broadcasts are forwarded• Local traffic stays local• Checks Layer 2 MAC
addresses in 802.3 frame
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Switches• Layer 2 device• Learns MAC addresses of
devices attached to each port• Each switchport is a collision
domain• More collision domains BUT
smaller collision domains• Broadcasts still sent out of
every port• Each switchport has dedicated
bandwidth• 100% bandwidth available
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Today’s LANs
Router
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Elements of Ethernet/802.3 networks
• Broadcast data frame delivery of Ethernet/802.3 • The carrier sense multiple access/collision detect (CSMA/CD) method
allows only one station to transmit at a time. • Multimedia applications with higher bandwidth demand such as video
and the Internet, coupled with the broadcast nature of Ethernet, can create network congestion.
• Normal latency as the frames travel across the layers• Extending the distances and increasing latency of the Ethernet/802.3
LANs by using Layer 1 repeaters.
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Transmission Time & Latency• Bit time – time taken to recognise 1 bit• Minimum frame size - 64 bytes – 512 bits• Maximum frame size – 1518 bytes – 12,144 bits• Transmission time is always 512 bit times• 10Mbps – 64 byte frame - 51,200 ns (100ns bit time)• 100Mbps – 64 byte frame 5,120 ns (10 ns bit time)• 1000Mbps – 64 byte frame – 512 ns (1ns bit time)
Times above do not include • Time taken to propagate signal along medium• Delays introduced by hubs/switches/routers/NICs etc
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Types of TransmissionHalf-duplex• Host checks medium
for signal – if clear host transmits
• Only 1 host can transmit at a time
• Collisions – jam signal generated, back-off algorithm before retransmission
• 50-60% bandwidth available
Full duplex• Host can transmit
immediately• 2 hosts can transmit
simultaneously• No collisions• 100% bandwidth
available• Requires dedicated
connection to a switchport
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Switching Concepts
Introduction to LAN Switching Switch Operation
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Overview• Maximum availability for the least cost
– Reduce the effects of collisions on available bandwidth
– Reduce the effect of broadcasts on available bandwidth
– Deploy network hardware (media/switches/routers) to overcome bottlenecks & meet bandwidth requirements
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Segmentation - bridges• A bridge splits a LAN into
2 segments• It creates 2 collision
domains• Adds 10-30% latency• Learns MAC addresses• Keeps local traffic local• Forwards broadcasts
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Segmentation With Bridges
•Segmentation provides fewer uses per segment•Bridges store, then forward frames based on Layer 2 addresses (CRC verified)•Layer 3 protocol-independent•Increase latency on the network
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Segmentation - Switches• Each switchport is a
collision domain – “micro-segmentation”
• 100% bandwidth available to each switchport
• Every switchport can send/receive simultaneously
• Host to switch/switch to switch connection creates full duplex link
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Segmentation With Routers
•More manageable, greater functionality, multiple active paths•Smaller broadcast domains•Operates at Layer 3
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Switch Operation - 1• When a switch starts up it sends a broadcast out
of all ports to learn host MAC addresses• When a frame is received for an unknown
destination a broadcast is sent to discover• Addresses are added to a switching table
mapping them to the port on which they were learned
• When a frame is received for a known destination it is switched to the appropriate port
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
LAN Switch Operation - 2• Switches contain RAM – known as CAM
“Content Addressable Memory”• Stores MAC address table• Used as frame buffer• Used to queue frames in asymmetric switching –
switchports operating at different speeds e.g. 10 and 100 Mbps
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Switching MethodsCut-through Switching• Fast-forward – as soon as destination address is read
switching starts• Fragment-free – after 64 bytes have been received
(minimum valid frame size) frame is switchedStore & Forward Switching• Entire frame is received before switching In
crea
sed
Late
ncy
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Terminology• Ignoring a frame – filtering• Copying a frame – forwarding• Microsegmentation – dividing a network into
smaller segments (using a switch)
CCNA3: Switching Basics and Intermediate Routing v3.0
CISCO NETWORKING ACADEMY PROGRAM
Chapter 4 – Switching Concepts
Broadcasts• Bridges & switches cannot block layer 2 or layer
3 broadcasts• Adding bridges or switches to a network extends
the broadcast domain but creates additional collision domains – a 24 port switch creates 24 collision domains
• Routers can inspect layer 3 packets and create broadcast domains – a router with 3 ports creates 3 broadcast domains