www.ciscopress.com copyright 2003 ccna 1 chapter 6, part 2 ethernet switching by your name
TRANSCRIPT
www.ciscopress.comCopyright 2003
CCNA 1 Chapter 6, part 2
Ethernet Switching
By
Your Name
www.ciscopress.comCopyright 2003
Objectives
• Ethernet switching
• Collision domains and broadcast domains
www.ciscopress.comCopyright 2003
Layer 2 Bridging
• Based on the Ethernet frame design, the need arose for a device that could hold a learned list of MAC addresses and direct frames to a specific port, based on the MAC address of the destination node.
• Describe the process.
www.ciscopress.comCopyright 2003
Bridge Types
A bridge connects network segments and makes intelligent decisions about whether to pass signals on to the next segment.
Source route bridges are used primarily with Token Ring network segments.
www.ciscopress.comCopyright 2003
Bridge Operations
www.ciscopress.comCopyright 2003
Switches
www.ciscopress.comCopyright 2003
Switch Benefits
www.ciscopress.comCopyright 2003
Switching Table
www.ciscopress.comCopyright 2003
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.
www.ciscopress.comCopyright 2003
Switch Modes
• Cut-through switching — A switch can start to transfer the frame as soon as the destination MAC address is received.
• Store-and-forward switching — The switch can receive the entire frame before sending it out the destination port. This gives the switch software an opportunity to verify the frame check sum (FCS).
www.ciscopress.comCopyright 2003
Spanning Tree Protocol
• Loops can occur when extra switches and bridges are added to provide redundant paths for reliability and fault tolerance.
• A switch sends special messages called bridge protocol data units (BPDUs) out all its ports to let other switches know of its existence.
• The switches use a spanning-tree algorithm (STA) to resolve and shut down the redundant paths
• The protocol used to resolve and eliminate loops is known as
the Spanning Tree Protocol (STP).
www.ciscopress.comCopyright 2003
Collision Domains and Broadcast Domains
www.ciscopress.comCopyright 2003
Shared Media Environments
• It is important to be able to identify a shared media environment, because collisions only occur in a shared environment.
• Some networks are directly connected and all hosts share Layer 1:– Shared media– Extended shared media– Point-to-point network
www.ciscopress.comCopyright 2003
Collisions and Collision Domains
• Shared media environment• Collisions and collision domains• Signals in a collision• Repeaters, hubs, and collision domains• The four-repeater rule• Segmenting collision domains
www.ciscopress.comCopyright 2003
Types of Networks
www.ciscopress.comCopyright 2003
Data Collisions
When two bits are propagated at the same time on the same network, a collision will occur.
www.ciscopress.comCopyright 2003
Collisions and Collision Domains
• Collisions are not inherently bad.– They are a normal function of Legacy Ethernet.
• Data on the network during a collision is lost and usually must be retransmitted.– Increased collisions indicate congestion.
• All devices on a network that would cause a collision if they transmitted simultaneously are in a collision domain.
• Networks with only Layer 1 components are a single collision domain.
www.ciscopress.comCopyright 2003
Shared Media, Repeaters, Hubs, and Collision Domains
Shared media
Extended by a repeater
Extended by a hub
Extended by a huband repeater
Each is a single collision domain!
www.ciscopress.comCopyright 2003
The Four-Repeater Rule
Legacy Ethernet network: No more than 4 repeaters or repeating hubs can be between any 2 computers on the network.– From A to B is 4 repeaters.
A
B
www.ciscopress.comCopyright 2003
Four-Repeater Rule Example
• The 5-story building shown violates the four-repeater rule because host A and B are 5 repeaters apart.
• Hubs would cause the same result.
• Even if all servers were on the third floor, and A and B would never communicate directly; they are too far to hear each other transmit and can cause data collisions.
• What are implications for taller buildings?
A
B
www.ciscopress.comCopyright 2003
Four-Repeater Rule Example Layer 1 Solution
• The hub added, which could be on any floor, allows us to comply with the four-repeater rule.
• No 2 hosts are more than 3 repeaters apart.
• What are implications for taller buildings? It really wouldn’t matter if each floor connects to the hub.
• How many collision domains do we have? Still only one and getting bigger with each floor.
A
B
Hub
www.ciscopress.comCopyright 2003
Too Much Traffic / Too Many Hosts in a Collision Domain…
www.ciscopress.comCopyright 2003
Ethernet LAN Segmentation
www.ciscopress.comCopyright 2003
Segmenting with Bridges
www.ciscopress.comCopyright 2003
Segmenting with Switches
www.ciscopress.comCopyright 2003
Segmenting with Routers
www.ciscopress.comCopyright 2003
Microsegmentation
Hubs
www.ciscopress.comCopyright 2003
Layer 2 Broadcasts
• Layer 2 devices must flood all broadcast and multicast traffic.
• The accumulation of broadcast and multicast traffic from each device in the network is referred to as broadcast radiation.
www.ciscopress.comCopyright 2003
The only devices that can segment collision domains are bridges, switches (both Layer 2), and routers (Layer 3).
Broadcast Domains
www.ciscopress.comCopyright 2003
Data Flow
www.ciscopress.comCopyright 2003
Network Segment
• If the segment is used in TCP, it would be defined as a separate piece of the data.
• If segment is being used in the context of physical networking media in a routed network, it would be seen as one of the parts or sections of the total network.