SRWE_Module_2.pdf

Module 2: Switching Concepts Instructor Materials Switching, Routing, and Wireless Essentials v7.0 (SRWE) What to Expect in this Module § To facilitate learning, the following features within the GUI may be included in this module: Feature Description Animations...

Module 2: Switching Concepts Instructor Materials Switching, Routing, and Wireless Essentials v7.0 (SRWE) What to Expect in this Module § To facilitate learning, the following features within the GUI may be included in this module: Feature Description Animations Expose learners to new skills and concepts. Expose learners to new skills and concepts. Videos Check Your Per topic online quiz to help learners gauge content understanding. Understanding(CYU) Interactive Activities A variety of formats to help learners gauge content understanding. Small simulations that expose learners to Cisco command line to practice Syntax Checker configuration skills. Simulation and modeling activities designed to explore, acquire, reinforce, and PT Activity expand skills. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 What to Expect in this Module (Cont.) § To facilitate learning, the following features may be included in this module: Feature Description Hands-On Labs Labs designed for working with physical equipment. Class Activities These are found on the Instructor Resources page. Class Activities are designed to facilitate learning, class discussion, and collaboration. Self-assessments that integrate concepts and skills learned throughout the Module Quizzes series of topics presented in the module. Module Summary Briefly recaps module content. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 Module 2: Switching Concepts Switching, Routing, and Wireless Essentials v7.0 (SRWE) Module Objectives Module Title: Switching Concepts Module Objective: Explain how Layer 2 switches forward data. Topic Title Topic Objective Frame Forwarding Explain how frames are forwarded in a switched network. Switching Domains Compare a collision domain to a broadcast domain. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 2.1 Frame Forwarding © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12 Frame Forwarding Switching in Networking Two terms are associated with frames entering or leaving an interface: Ingress – entering the interface Egress – exiting the interface A switch forwards based on the ingress interface and the destination MAC address. A switch uses its MAC address table to make forwarding decisions. Note: A switch will never allow traffic to be forwarded out the interface it received the traffic. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13 Frame Forwarding The Switch MAC Address Table A switch will use the destination MAC address to determine the egress interface. Before a switch can make this decision it must learn what interface the destination is located. A switch builds a MAC address table, also known as a Content Addressable Memory (CAM) table, by recording the source MAC address into the table along with the port it was received. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14 Frame Forwarding The Switch Learn and Forward Method The switch uses a two step process: Step 1. Learn – Examines Source Address Adds the source MAC if not in table Resets the time out setting back to 5 minutes if source is in the table Step 2. Forward – Examines Destination Address If the destination MAC is in the MAC address table it is forwarded out the specified port. If a destination MAC is not in the table, it is flooded out all interfaces except the one it was received. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15 Frame Forwarding Video – MAC Address Tables on Connected Switches This video will cover the following: How switches build MAC address tables How switches forward frames based on the content of their MAC address tables © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16 Frame Forwarding Switch Forwarding Methods Switches use software on application-specific-integrated circuits (ASICs) to make very quick decisions. A switch will use one of two methods to make forwarding decisions after it receives a frame: Store-and-forward switching - Receives the entire frame and ensures the frame is valid. Store-and-forward switching is Cisco’s preferred switching method. Cut-through switching – Forwards the frame immediately after determining the destination MAC address of an incoming frame and the egress port. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17 Frame Forwarding Store-and-Forward Switching Store-and-forward has two primary characteristics: Error Checking – The switch will check the Frame Check Sequence (FCS) for CRC errors. Bad frames will be discarded. Buffering – The ingress interface will buffer the frame while it checks the FCS. This also allows the switch to adjust to a potential difference in speeds between the ingress and egress ports. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18 Frame Forwarding Cut-Through Switching Cut-through forwards the frame immediately after determining the destination MAC. Fragment (Frag) Free method will check the destination and ensure that the frame is at least 64 Bytes. This will eliminate runts. Concepts of Cut-Through switching: Is appropriate for switches needing latency to be under 10 microseconds Does not check the FCS, so it can propagate errors May lead to bandwidth issues if the switch propagates too many errors Cannot support ports with differing speeds going from ingress to egress © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19 2.2 Switching Domains © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 20 Switching Domains Collision Domains Switches eliminate collision domains and reduce congestion. When there is full duplex on the link the collision domains are eliminated. When there is one or more devices in half-duplex there will now be a collision domain. There will now be contention for the bandwidth. Collisions are now possible. Most devices, including Cisco and Microsoft use auto-negotiation as the default setting for duplex and speed. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 Switching Domains Broadcast Domains A broadcast domain extends across all Layer 1 or Layer 2 devices on a LAN. Only a layer 3 device (router) will break the broadcast domain, also called a MAC broadcast domain. The broadcast domain consists of all devices on the LAN that receive the broadcast traffic. When the layer 2 switch receives the broadcast it will flood it out all interfaces except for the ingress interface. Too many broadcasts may cause congestion and poor network performance. Increasing devices at Layer 1 or layer 2 will cause the broadcast domain to expand. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22 Switching Domains Alleviated Network Congestion Switches use the MAC address table and full-duplex to eliminate collisions and avoid congestion. Features of the switch that alleviate congestion are as follows: Protocol Function Fast Port Speeds Depending on the model, switches may have up to 100Gbps port speeds. Fast Internal Switching This uses fast internal bus or shared memory to improve performance. Large Frame Buffers This allows for temporary storage while processing large quantities of frames. High Port Density This provides many ports for devices to be connected to LAN with less cost. This also provides for more local traffic with less congestion. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23 2.3 Module Practice and Quiz © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 24 Module Practice and Quiz What did I learn in this module? Frame Forwarding Ingress is the entry port, egress is the exit port. The switch builds a MAC address table to forward frames on the LAN. The switch can use either the store-and-forward or cut-through method of switch forwarding. Switching Domains Ethernet ports in half-duplex will be a part of a collision domain. Full-duplex will eliminate collision domains. A switch will flood out all interfaces except the ingress port if the frame is a broadcast or if the unicast destination MAC is unknown. Broadcast domains may be broken up by a layer 3 device, like a router. Switches extend broadcast domains, but can eliminate collision domains and relieve congestion. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 25