Copyright 2003 CCNA 1 Chapter 6, part 2 Ethernet Switching By Your Name

Copyright 2003 Objectives Ethernet switching Collision domains and broadcast domains

Copyright 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.

Copyright 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.

Copyright 2003 Bridge Operations

Copyright 2003 Switches

Copyright 2003 Switch Benefits

Copyright 2003 Switching Table

Copyright 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.

Copyright 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).

Copyright 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).

Copyright 2003 Collision Domains and Broadcast Domains

Copyright 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

Copyright 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

Copyright 2003 Types of Networks

Copyright 2003 Data Collisions When two bits are propagated at the same time on the same network, a collision will occur.

Copyright 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.

Copyright 2003 Shared Media, Repeaters, Hubs, and Collision Domains Shared media Extended by a repeater Extended by a hub Extended by a hub and repeater Each is a single collision domain!

Copyright 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

Copyright 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

Copyright 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

Copyright 2003 Too Much Traffic / Too Many Hosts in a Collision Domain…

Copyright 2003 Ethernet LAN Segmentation

Copyright 2003 Segmenting with Bridges

Copyright 2003 Segmenting with Switches

Copyright 2003 Segmenting with Routers

Copyright 2003 Microsegmentation Hubs

Copyright 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.

Copyright 2003 The only devices that can segment collision domains are bridges, switches (both Layer 2), and routers (Layer 3). Broadcast Domains

Copyright 2003 Data Flow

Copyright 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.