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Chapter 12 Basic Switching and Switch Configuration

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  • Chapter 12Basic Switching and Switch Configuration

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  • CCNA Guide to Cisco Networking Fundamentals*ObjectivesExplain the technology and media access control method for Ethernet networksExplain network segmentation and basic traffic management conceptsExplain basic switching concepts and the operation of Cisco switchesPerform and verify switch configuration tasksImplement basic switch security

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Ethernet OperationsEthernetA network access method (or media access method) originated by the University of Hawaii, later adopted by Xerox CorporationAnd standardized as IEEE 802.3 in the early 1980sEthernet is:Most pervasive network access method in useMost commonly implemented media access method in new LANs

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*CSMA/CDCarrier Sense Multiple Access with Collision Detection (CSMA/CD)Ethernet contention methodAny station connected to a network can transmit anytime a transmission is not present on the wireInterframe gap, or interpacket gap (IPG)After each transmitted signal, each station must wait a minimum of 9.6 microseconds before transmitting another packet

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*CSMA/CD (continued)CollisionsTwo stations could listen to the wire simultaneously and not sense a carrier signalBoth stations might begin to transmit their data simultaneouslyOnce a collision is detected, the first station to detect the collision transmits a 32-bit jam signalTells all other stations not to transmit for a brief periodThe two stations that caused the collision use an algorithm to enter a backoff period

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*CSMA/CD (continued)Collision domainThe physical area in which a packet collision might occurRouters, switches, bridges, and gateways segment networksAnd thus create separate collision domainsThe 32-bit jam signal that is transmitted when the collision is discovered prevents all stations on that collision domain from transmitting

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*CSMA/CD (continued)BroadcastsStations on a network broadcast packets to other stations to make their presence known on the network And to carry out normal network tasksWhen a segment has too much broadcast traffic:Utilization increasesNetwork performance in general suffersSimple ways to reduce broadcast traffic:Reduce the number of services on your networkLimit the number of protocols in use on your network

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*CSMA/CD (continued)Broadcast stormA sudden rush of network transmissions that causes all other network communications to slow downDue to the volume of data competing for access to the same bandwidth on the communications mediumOne of the most common causes of broadcast storms is a network loop

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*LatencyLatency, or propagation delayThe length of time that is required to forward, send, or otherwise propagate a data frameLatency differs depending on the resistance offered by the transmission medium, the number of nodes And in the case of a connectivity device, the amount of processing that must be done on the packetTransmission timeThe amount of time it takes for a packet to be sent from one device to another

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Latency (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Latency (continued)Bit timeRefers to the amount of time required to transmit one data bit on a networkSlot time (512 bit times)An important specification that limits the physical size of each Ethernet collision domainSpecifies that all collisions should be detected from anywhere in a network in less time than is required to place a 64-byte frame on the network

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Ethernet ErrorsFrame size errorsShort frame or runtLong frame or giantJabberFrame check sequence (FCS) errorIndicates that bits of a frame were corrupted during transmissionCan be caused by any of the previously listed errors

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Ethernet Errors (continued)Collision errorsReducing the number of devices per collision domain will usually solve the problemYou can do this by segmenting your network with a router, a bridge, or a switchLate collisionOccurs when two stations transmit more than 64 bytes of data frames before detecting a collision

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Ethernet Errors (continued)Fast EthernetUses the same CSMA/CD as common 10BaseT EthernetProvides ten times the data transmission rate100 MbpsDefined under the IEEE 802.3u standardImplementations100Base-TX100Base-T4100Base-FX

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Gigabit EthernetRecent advances in technology have allowed us to reach even higher speeds than those of Fast EthernetGigabit Ethernet implementations1000Base-TX (802.3ab)1000Base-SX (802.3z)1000Base-LX (802.3z)1000Base-CX (802.3z)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Half- and Full-Duplex CommunicationsHalf-duplex communicationsDevices can send and receive signals, but not at the same timeFull-duplex (or duplex) communicationsDevices can send and receive signals simultaneouslyEthernet networks can use equipment that supports half- and full-duplex communications

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Half- and Full-Duplex Communications (continued)Benefits of using full-duplex:Time is not wasted retransmitting frames because collisions do not occurThe full bandwidth is available in both directions because the send and receive functions are separateStations do not have to wait until other stations complete their transmissions because only one transmitter is used for each twisted pair

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Half- and Full-Duplex Communications (continued)On a Cisco Catalyst 2950 switch, you can set the duplex capabilities port-by-portThe four different duplex options are:AutoFullFull-flow controlHalf

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*A Review of LAN SegmentationYou can improve the performance of your Ethernet networkBy reducing the number of stations per collision domainTypically, network administrators implement bridges, switches, or routers to segment the network and divide the collision domains

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with BridgesBridgeSegments a network by filtering traffic at the Data Link layerDivides a network into two or more segmentsOnly forwards a frame from one segment to another if the frame is a broadcast or has the MAC address of a station on a different segmentBridges learn MAC addresses by reading the source MAC addresses from framesAs the frames are passed across the bridge

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with Bridges (continued)Bridging tableMaps the MAC addresses on each segment to the corresponding port on the bridge to which each segment is connectedBridges increase latency, but because they effectively divide the collision domainThis does not affect slot time

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with Bridges (continued)Remember these points:Bridges reduce collisions on the LAN and filter traffic based on MAC addressesA bridge does not reduce broadcast or multicast trafficA bridge can extend the useful distance of the Ethernet LANThe bandwidth for the new individual segments is increasedBridges can be used to limit traffic for security purposes

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with RoutersRouterOperates at layer 3 of the OSI reference modelInterprets the Network layer protocol and makes forwarding decisions based on the layer 3 addressRouters typically do not propagate broadcast trafficThus, they reduce network traffic even more than bridges doRouters maintain routing tables that include the Network layer addresses of different segments

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with Routers (continued)When you segment a LAN with routers, they will:Decrease collisions by filtering trafficReduce broadcast and multicast traffic by blocking or selectively filtering packetsSupport multiple paths and routes between themProvide increased bandwidth for the newly created segmentsIncrease security by preventing packets between hosts on one side of the router from propagating to the other side of the router

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmenting with Routers (continued)When you segment a LAN with routers, they will: (continued)Increase the effective distance of the network by creating new collision domainsProvide layer 3 routing, packet fragmentation and reassembly, and traffic flow controlProvide communications between different technologies, such as Ethernet and Token Ring or Ethernet and Frame RelayHave a higher latency than bridges, because routers have more to process; faster processors in the router can reduce some of this latency

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*LAN SwitchingSwitchesSimilar to bridges in several waysUsing a switch on a LAN has a different effect on the way network traffic is propagated

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmentation with SwitchesSwitches are often called multiport bridgesSwitch typically connects multiple stations individuallyThereby segmenting a LAN into multiple collision domainsSwitches microsegment the networkBy connecting each port to an individual workstationSwitched bandwidthBandwidth is not shared as long as each workstation connects to its own switch port

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmentation with Switches (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Segmentation with Switches (continued)Switch latency is typically higher than that of a repeater or hubFaster processors and a variety of switching techniques make switches typically faster than bridgesSwitches provide the following benefits:Reduction in network traffic and collisionsIncrease in available bandwidth per stationIncrease in the effective distance of a LAN by dividing it into multiple collision domainsIncreased security, because unicast traffic is sent directly to its destination

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Switch OperationsA switch learns the hardware address of devices to which it is attachedBy reading the source address of frames as they are transmitted across the switchThe switch then matches the source MAC address with the port from which the frame was sentThe MAC-to-switch-port mapping is stored in the switchs content-addressable memory (CAM)The switch uses a memory buffer to store frames as it determines to which port(s) a frame will be forwarded

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Switch Operations (continued)Types of memory buffering: Port-based memory bufferingShared memory bufferingAsymmetric switchingSome switches can interconnect network interfaces of different speedsSymmetric switchingSwitches that require all attached network interface devices to use the same transmit/receive speed

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Switching MethodsAll switches base frame-forwarding decisions on a frames destination MAC addressThe three main methods for processing and forwarding frames are:Cut-through, store-and-forward, and fragment-freeOne additional forwarding method, adaptive cut-through forwardingA combination of the cut-through and store-and-forward methods

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Switching Methods (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Cut-Through ForwardingSwitches that use cut-through forwarding start sending a frame immediately after reading the destination MAC address into their buffersThe main benefit of cut-through forwarding is a reduction in latencyThe drawback is the potential for errors in the frame that the switch would be unable to detectBecause the switch only reads a small portion of the frame into its buffer

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Cut-Through Forwarding (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Store-and-Forward ForwardingStore-and-forward switches read the entire frame, no matter how large, into their buffers before forwardingBecause the switch reads the entire frame, it will not forward frames with errorsThe store-and-forward method has the highest latency

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Store-and-Forward Forwarding (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Fragment-Free ForwardingFragment-free forwarding represents an effort to provide more error-reducing benefits than cut-through switchingWhile keeping latency lower than does store-and-forward switchingA fragment-free switch reads the first 64 bytes of an Ethernet frameAnd then begins forwarding it to the appropriate port(s)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Fragment-Free Forwarding (continued)

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Fragment-Free Forwarding (continued)Adaptive cut-throughFor the most part, the adaptive cut-through switch will act as a cut-through switchTo provide the lowest latencyHowever, if a certain level of errors is detected, the switch will:Change forwarding techniquesAct more as a store-and-forward switch

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Switch User InterfaceTwo types of operating systems are in use on Cisco switches: IOS-based and set-basedYou can connect to a Cisco switch in the same way you connect to a Cisco routerThe Cisco switch has a console port to which you can connect your laptop or PCOnce you power on the switch you will be in the command-line interfaceYou can configure anything from the command line

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Modes and PasswordsYou cannot actually configure a switch until you get to enable modeTo enter enable mode, type enable at the command-line prompt and then press EnterThe first step in configuring a switch is to set up a passwordTo start configuration mode, first type configure terminal or config t at the command promptYou can also configure a secret (encrypted) password

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Setting the Host NameThe actual task of setting the host name on the Cisco Catalyst switch is identical to setting the host name on a Cisco routerTo configure this name, you would type:Switch(config)#hostname nameOnce the host name is set, the prompt will change to reflect the name of the switch

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*IP on the SwitchBy default, Cisco switches are not configured with IP addressesGenerally speaking, a switch does not require an IP addressBecause switches operate mainly on Layer 2You may want to configure an IP address for your switch so that you can manage it over the network Also, you may need to configure an IP address for your switch if you want to implement VLANs on your network

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Configuring Switch PortsTo enter interface configuration mode for the first port of a switch named Rm410HL, you would use the following commands:Rm410HL#configure terminalRm410HL(config)#interface f0/1Rm410HL(config-if)#To view the configuration of a port, use the show command

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Configuring Switch Ports (continued)Configuring the duplex modeYou would use the following command to set the duplex mode:Rm410HL#configure terminalRm410HL(config)#interface f0/24Rm410HL(config-if)#duplex full

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Securing Switch PortsYou can choose from several degrees of security on a switchFirst, you can configure a permanent MAC address for a specific port on your switchSecond, you could define a static MAC address entry into your switching tableWhich maps a restricted communication path between two portsTo configure port security, you first must enter the interface configuration mode

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Securing Switch Ports (continued)You can display several options by typing the following command:Rm410HL(config-if)#switchport port-security ?Options include aging, mac-address, maximum, and violationTo turn switchport security off, use:Rm410HL(config-if)#no switchport port-securityTo clear the settings to include erasing the static MAC addresses, use the clear command:Rm410HL(config-if)#clear port-security

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*SummaryEthernet (CSMA/CD) is a media access method that was developed in the 1960sStations on an Ethernet LAN must listen to the network media before transmitting to ensure that no other station is currently transmittingIf two stations transmit simultaneously on the same collision domain, a collision will occurThe transmitting stations must be able to recognize the collision and ensure that other stations know about it by transmitting a jam signal

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Summary (continued)The delays caused by collisions on a network can seriously affect performance when collisions exceed 5% of the traffic on the collision domainSwitches do the most to divide the collision domain and reduce traffic without dividing the broadcast domainA switch microsegments unicast trafficAnother way to increase the speed at which a LAN operates is to upgrade from Ethernet to Fast EthernetFull duplex can also improve Ethernet performance

    CCNA Guide to Cisco Networking Fundamentals*

  • CCNA Guide to Cisco Networking Fundamentals*Summary (continued)Full duplex allows frames to be sent and received simultaneouslyAs with Fast Ethernet, full-duplex operations are only supported by devices designed for this type of communicationThe two types of operating systems on Cisco switches are IOS-based and set-basedConfiguring a switch is similar to configuring a router through the CLISwitches can provide some level of security through the use of port security commands

    CCNA Guide to Cisco Networking Fundamentals*

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