Tài liệu giảng dạy CCNA - module 04 chapter 13-Cisco LAN Switching Basics

Module 04 LAN Switching Chapter 13 Cisco LAN Switching Basics Table of Content The Case for Bridging and Switching LAN Switching LAN Segmentation The Need for Spanning Tree The Case for Bridging and Switching Collisions domain: Share access  Limits the number of computers Collisions domain: Repeater  Propagate collisions Collisions domain: HUB  Propagate collisions Collisions domain  Collision Domains are the area where collisions occur  All of layer interconnections are part of the collision domain  Extending a network with a repeater or a hub, results in a larger collision domain Segmenting Collision Domain LAN Segmentation With Bridges Layer bridging 00000CAAAAAA 00000CAAAAAA 00000CDDDDD 00000CBBBBBB A B MAC Address 00000CAAAAAA 00000CBBBBBB 00000CCCCCCC 00000CDDDDDD Port 2 00000CCCCCCC C 00000CDDDDDD D LAN Segmentation With Routers LAN Segmentation With Switches • Switches eliminate the impacts of collisions through the micro-segmentation • Work with existing 802.3(CSMA/CD) Switches And Collision Domains  The network area where frames originate and collide is called the collision domain  A switch builds a switching table by learning the MAC addresses of the hosts that are connected to each switch port  When two connected hosts want to communicate with each other, the switch looks up the switching table and establishes a virtual connection between the ports  The virtual circuit is maintained until the session is terminated Switches And Broadcast Domains  Broadcasting is when one transmitter tries to reach all the receivers in the network  When a device wants to send out a Layer broadcast, the destination MAC address in the frame is set to all ones  The broadcast domain at Layer in referred to as the MAC broadcast domain  The MAC broadcast domain consists of all devices on the LAN that receive frame broadcasts by a host to all other machines on the LAN The Need for Spanning Tree Redundant topology and spanning tree  Redundant networking topologies are designed to ensure that networks continue to function in the presence of single points of failure  Switches flood traffic out all ports when the traffic is broadcast or multicast or sent to a destination that is not yet known  In the Layer header there is no Time To Live (TTL) If a frame is sent into a Layer looped topology of switches, it can loop forever The solution is to allow physical loops, but create a loop free logical topology Spanning Tree Protocol  The ST Algorithm, implemented by the STP, prevents loops by calculating a stable spanning-tree network topology  Spanning-tree frames, called bridge protocol data units (BPDUs), are sent and received by all switches in the network at regular intervals and are used to determine the spanning-tree topology STP port status  Blocking:  No frames forwarded, BPDUs heard  Listening:  No frames forwarded, listening for frames  Learning:  No frames forwarded, learning addresses  Forwarding:  Frames forwarded, learning addresses  Disabled:  No frames forwarded, no BPDUs heard Algorithm  All bridge interfaces eventually stabilize at either a forwarding or a blocking  One of the bridges is elected as root  All root bridge interfaces are in forwarding  Each bridge receives BPDU from the root, either directly or forwarded by some other bridge  The port in which the least-cost BPDU is received is called the root port of a bridge is placed in forwarding Root Bridge Bridge MAC: 1111.1111.1111 Priority: 32768 Root Bridge Root Port Root Port Bridge MAC: AAAA.AAAA.AAAA Priority: 32768 Bridge MAC: 8888.8888.8888 Priority: 32768 Algorithm (cont.)  For each LAN segment:  Designated bridge is one bridge sends the forwarded BPDU with the lowest cost  The designated bridge’s interface is placed in forwarding state  All interfaces of other bridges are placed in blocking state Port Cost  – 65535  Default port cost for Ethernet:  10Mbps: 100  100Mbps: 19  1Gbps:  10Gbps:2 Designated Bridge Bridge MAC: 1111.1111.1111 Priority: 32768 Root Bridge Port: 100Mbps Port: 10Mbps Cost 19 Bridge MAC: AAAA.AAAA.AAAA Priority: 32768 Cost 100 Bridge MAC: 8888.8888.8888 Priority: 32768 Algorithm (cont.)  Hello Time (2s):  The root sends BPDU every Hello time  All bridges use the same value  MaxAge time (20s):  If a bridge does not receive a BPDU for MaxAge time It begins the process of causing the Spanning Tree to change  Forward Delay time (15s):  Listening time between blocking and forwarding After that, the state is changed to learning Summary  LAN segmentation with bridges, switches, routers  Spanning Tree Protocol ... and Fragment-free switching 3 LAN Segmentation LAN Segmentation Isolate traffic between segment achieve more bandwidth LAN Segmentation With Bridges LAN Segmentation With Routers LAN Segmentation... the LAN not behave any differently in the presence or absence of transparent bridges 2 LAN Switching Switch operation      A multi port bridge Micro-segment Support full duplex Hardware switching. .. maintains a Content-Addressable Memory (CAM) table Half-duplex Networks Full-duplex Transmitting 10 or 100 Mbps 10 or 100 Mbps Full-Duplex 10 or 100 Mbps 10 or 100 Mbps  Full-duplex Ethernet