CCNA SWITCHING AND CONFIGURATION

CCNA SWITCHING AND CONFIGURATION

• 1.
  CCNA Guide toCisco Networking Fundamentals Chapter 12 Basic Switching and Switch Configuration
• 2.
  CCNA Guide toCisco Networking Fundamentals 2 Objectives • Explain the technology and media access control method for Ethernet networks • Explain network segmentation and basic traffic management concepts • Explain basic switching concepts and the operation of Cisco switches • Perform and verify switch configuration tasks • Implement basic switch security
• 3.
  CCNA Guide toCisco Networking Fundamentals 3 Ethernet Operations • Ethernet – A network access method (or media access method) originated by the University of Hawaii, later adopted by Xerox Corporation – And standardized as IEEE 802.3 in the early 1980s • Ethernet is: – Most pervasive network access method in use – Most commonly implemented media access method in new LANs
• 4.
  CCNA Guide toCisco Networking Fundamentals 4 CSMA/CD • Carrier Sense Multiple Access with Collision Detection (CSMA/CD) – Ethernet contention method • Any station connected to a network can transmit anytime a transmission is not present on the wire • Interframe gap, or interpacket gap (IPG) – After each transmitted signal, each station must wait a minimum of 9.6 microseconds before transmitting another packet
• 5.
  CCNA Guide toCisco Networking Fundamentals 5 CSMA/CD (continued) • Collisions – Two stations could listen to the wire simultaneously and not sense a carrier signal – Both stations might begin to transmit their data simultaneously – Once a collision is detected, the first station to detect the collision transmits a 32-bit jam signal • Tells all other stations not to transmit for a brief period – The two stations that caused the collision use an algorithm to enter a backoff period
• 6.
  CCNA Guide toCisco Networking Fundamentals 6 CSMA/CD (continued) • Collision domain – The physical area in which a packet collision might occur – Routers, switches, bridges, and gateways segment networks • And thus create separate collision domains – The 32-bit jam signal that is transmitted when the collision is discovered prevents all stations on that collision domain from transmitting
• 7.
  CCNA Guide toCisco Networking Fundamentals 7 CSMA/CD (continued) • Broadcasts – Stations on a network broadcast packets to other stations to make their presence known on the network • And to carry out normal network tasks – When a segment has too much broadcast traffic: • Utilization increases • Network performance in general suffers – Simple ways to reduce broadcast traffic: • Reduce the number of services on your network • Limit the number of protocols in use on your network
• 8.
  CCNA Guide toCisco Networking Fundamentals 8 CSMA/CD (continued) • Broadcast storm – A sudden rush of network transmissions that causes all other network communications to slow down • Due to the volume of data competing for access to the same bandwidth on the communications medium • One of the most common causes of broadcast storms is a network loop
• 9.
  CCNA Guide toCisco Networking Fundamentals 9 Latency • Latency, or propagation delay – The length of time that is required to forward, send, or otherwise propagate a data frame – Latency 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 packet • Transmission time – The amount of time it takes for a packet to be sent from one device to another
• 10.
  CCNA Guide toCisco Networking Fundamentals 10 Latency (continued)
• 11.
  CCNA Guide toCisco Networking Fundamentals 11 Latency (continued) • Bit time – Refers to the amount of time required to transmit one data bit on a network • Slot time (512 bit times) – An important specification that limits the physical size of each Ethernet collision domain – Specifies 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
• 12.
  CCNA Guide toCisco Networking Fundamentals 12 Ethernet Errors • Frame size errors – Short frame or runt – Long frame or giant – Jabber • Frame check sequence (FCS) error – Indicates that bits of a frame were corrupted during transmission – Can be caused by any of the previously listed errors
• 13.
  CCNA Guide toCisco Networking Fundamentals 13 Ethernet Errors (continued) • Collision errors – Reducing the number of devices per collision domain will usually solve the problem • You can do this by segmenting your network with a router, a bridge, or a switch – Late collision • Occurs when two stations transmit more than 64 bytes of data frames before detecting a collision
• 14.
  CCNA Guide toCisco Networking Fundamentals 14 Ethernet Errors (continued) • Fast Ethernet – Uses the same CSMA/CD as common 10BaseT Ethernet – Provides ten times the data transmission rate—100 Mbps – Defined under the IEEE 802.3u standard • Implementations – 100Base-TX – 100Base-T4 – 100Base-FX
• 15.
  CCNA Guide toCisco Networking Fundamentals 15 Gigabit Ethernet • Recent advances in technology have allowed us to reach even higher speeds than those of Fast Ethernet • Gigabit Ethernet implementations – 1000Base-TX (802.3ab) – 1000Base-SX (802.3z) – 1000Base-LX (802.3z) – 1000Base-CX (802.3z)
• 16.
  CCNA Guide toCisco Networking Fundamentals 16 Half- and Full-Duplex Communications • Half-duplex communications – Devices can send and receive signals, but not at the same time • Full-duplex (or duplex) communications – Devices can send and receive signals simultaneously • Ethernet networks can use equipment that supports half- and full-duplex communications
• 17.
  CCNA Guide toCisco Networking Fundamentals 17
• 18.
  CCNA Guide toCisco Networking Fundamentals 18 Half- and Full-Duplex Communications (continued) • Benefits of using full-duplex: – Time is not wasted retransmitting frames because collisions do not occur – The full bandwidth is available in both directions because the send and receive functions are separate – Stations do not have to wait until other stations complete their transmissions because only one transmitter is used for each twisted pair
• 19.
  CCNA Guide toCisco Networking Fundamentals 19 Half- and Full-Duplex Communications (continued) • On a Cisco Catalyst 2950 switch, you can set the duplex capabilities port-by-port • The four different duplex options are: – Auto – Full – Full-flow control – Half
• 20.
  CCNA Guide toCisco Networking Fundamentals 20 A Review of LAN Segmentation • You can improve the performance of your Ethernet network – By reducing the number of stations per collision domain • Typically, network administrators implement bridges, switches, or routers to segment the network and divide the collision domains
• 21.
  CCNA Guide toCisco Networking Fundamentals 21 Segmenting with Bridges • Bridge – Segments a network by filtering traffic at the Data Link layer – Divides a network into two or more segments • Only 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 segment • Bridges learn MAC addresses by reading the source MAC addresses from frames – As the frames are passed across the bridge
• 22.
  CCNA Guide toCisco Networking Fundamentals 22 Segmenting with Bridges (continued) • Bridging table – Maps the MAC addresses on each segment to the corresponding port on the bridge to which each segment is connected • Bridges increase latency, but because they effectively divide the collision domain – This does not affect slot time
• 23.
  CCNA Guide toCisco Networking Fundamentals 23 Segmenting with Bridges (continued) • Remember these points: – Bridges reduce collisions on the LAN and filter traffic based on MAC addresses – A bridge does not reduce broadcast or multicast traffic – A bridge can extend the useful distance of the Ethernet LAN – The bandwidth for the new individual segments is increased – Bridges can be used to limit traffic for security purposes
• 24.
  CCNA Guide toCisco Networking Fundamentals 24 Segmenting with Routers • Router – Operates at layer 3 of the OSI reference model – Interprets the Network layer protocol and makes forwarding decisions based on the layer 3 address • Routers typically do not propagate broadcast traffic – Thus, they reduce network traffic even more than bridges do • Routers maintain routing tables that include the Network layer addresses of different segments
• 25.
  CCNA Guide toCisco Networking Fundamentals 25 Segmenting with Routers (continued) • When you segment a LAN with routers, they will: – Decrease collisions by filtering traffic – Reduce broadcast and multicast traffic by blocking or selectively filtering packets – Support multiple paths and routes between them – Provide increased bandwidth for the newly created segments – Increase security by preventing packets between hosts on one side of the router from propagating to the other side of the router
• 26.
  CCNA Guide toCisco Networking Fundamentals 26 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 domains – Provide layer 3 routing, packet fragmentation and reassembly, and traffic flow control – Provide communications between different technologies, such as Ethernet and Token Ring or Ethernet and Frame Relay – Have a higher latency than bridges, because routers have more to process; faster processors in the router can reduce some of this latency
• 27.
  CCNA Guide toCisco Networking Fundamentals 27 LAN Switching • Switches – Similar to bridges in several ways • Using a switch on a LAN has a different effect on the way network traffic is propagated
• 28.
  CCNA Guide toCisco Networking Fundamentals 28 Segmentation with Switches • Switches are often called multiport bridges • Switch typically connects multiple stations individually – Thereby segmenting a LAN into multiple collision domains • Switches microsegment the network – By connecting each port to an individual workstation • Switched bandwidth – Bandwidth is not shared as long as each workstation connects to its own switch port
• 29.
  CCNA Guide toCisco Networking Fundamentals 29 Segmentation with Switches (continued)
• 30.
  CCNA Guide toCisco Networking Fundamentals 30
• 31.
  CCNA Guide toCisco Networking Fundamentals 31 Segmentation with Switches (continued) • Switch latency is typically higher than that of a repeater or hub – Faster processors and a variety of switching techniques make switches typically faster than bridges • Switches provide the following benefits: – Reduction in network traffic and collisions – Increase in available bandwidth per station – Increase in the effective distance of a LAN by dividing it into multiple collision domains – Increased security, because unicast traffic is sent directly to its destination
• 32.
  CCNA Guide toCisco Networking Fundamentals 32 Switch Operations • A switch learns the hardware address of devices to which it is attached – By reading the source address of frames as they are transmitted across the switch • The switch then matches the source MAC address with the port from which the frame was sent – The MAC-to-switch-port mapping is stored in the switch’s 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
• 33.
  CCNA Guide toCisco Networking Fundamentals 33 Switch Operations (continued) • Types of memory buffering: – Port-based memory buffering – Shared memory buffering • Asymmetric switching – Some switches can interconnect network interfaces of different speeds • Symmetric switching – Switches that require all attached network interface devices to use the same transmit/receive speed
• 34.
  CCNA Guide toCisco Networking Fundamentals 34 Switching Methods • All switches base frame-forwarding decisions on a frame’s destination MAC address • The three main methods for processing and forwarding frames are: – Cut-through, store-and-forward, and fragment-free • One additional forwarding method, adaptive cut- through forwarding – A combination of the cut-through and store-and- forward methods
• 35.
  CCNA Guide toCisco Networking Fundamentals 35 Switching Methods (continued)
• 36.
  CCNA Guide toCisco Networking Fundamentals 36 Cut-Through Forwarding • Switches that use cut-through forwarding start sending a frame immediately after reading the destination MAC address into their buffers • The main benefit of cut-through forwarding is a reduction in latency • The drawback is the potential for errors in the frame that the switch would be unable to detect – Because the switch only reads a small portion of the frame into its buffer
• 37.
  CCNA Guide toCisco Networking Fundamentals 37 Cut-Through Forwarding (continued)
• 38.
  CCNA Guide toCisco Networking Fundamentals 38 Store-and-Forward Forwarding • Store-and-forward switches read the entire frame, no matter how large, into their buffers before forwarding • Because the switch reads the entire frame, it will not forward frames with errors • The store-and-forward method has the highest latency
• 39.
  CCNA Guide toCisco Networking Fundamentals 39 Store-and-Forward Forwarding (continued)
• 40.
  CCNA Guide toCisco Networking Fundamentals 40 Fragment-Free Forwarding • Fragment-free forwarding represents an effort to provide more error-reducing benefits than cut- through switching – While keeping latency lower than does store-and- forward switching • A fragment-free switch reads the first 64 bytes of an Ethernet frame – And then begins forwarding it to the appropriate port(s)
• 41.
  CCNA Guide toCisco Networking Fundamentals 41 Fragment-Free Forwarding (continued)
• 42.
  CCNA Guide toCisco Networking Fundamentals 42 Fragment-Free Forwarding (continued) • Adaptive cut-through – For the most part, the adaptive cut-through switch will act as a cut-through switch • To provide the lowest latency – However, if a certain level of errors is detected, the switch will: • Change forwarding techniques • Act more as a store-and-forward switch
• 43.
  CCNA Guide toCisco Networking Fundamentals 43 Switch User Interface • Two types of operating systems are in use on Cisco switches: IOS-based and set-based • You can connect to a Cisco switch in the same way you connect to a Cisco router • The Cisco switch has a console port to which you can connect your laptop or PC • Once you power on the switch you will be in the command-line interface – You can configure anything from the command line
• 44.
  CCNA Guide toCisco Networking Fundamentals 44 Modes and Passwords • You cannot actually configure a switch until you get to enable mode • To enter enable mode, type enable at the command-line prompt and then press Enter • The first step in configuring a switch is to set up a password • To start configuration mode, first type configure terminal or config t at the command prompt • You can also configure a secret (encrypted) password
• 45.
  CCNA Guide toCisco Networking Fundamentals 45 Setting the Host Name • The actual task of setting the host name on the Cisco Catalyst switch is identical to setting the host name on a Cisco router • To configure this name, you would type: – Switch(config)#hostname name • Once the host name is set, the prompt will change to reflect the name of the switch
• 46.
  CCNA Guide toCisco Networking Fundamentals 46 IP on the Switch • By default, Cisco switches are not configured with IP addresses – Generally speaking, a switch does not require an IP address • Because switches operate mainly on Layer 2 • You 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
• 47.
  CCNA Guide toCisco Networking Fundamentals 47 Configuring Switch Ports • To enter interface configuration mode for the first port of a switch named Rm410HL, you would use the following commands: – Rm410HL#configure terminal – Rm410HL(config)#interface f0/1 – Rm410HL(config-if)# • To view the configuration of a port, use the show command
• 48.
  CCNA Guide toCisco Networking Fundamentals 48 Configuring Switch Ports (continued) • Configuring the duplex mode – You would use the following command to set the duplex mode: • Rm410HL#configure terminal • Rm410HL(config)#interface f0/24 • Rm410HL(config-if)#duplex full
• 49.
  CCNA Guide toCisco Networking Fundamentals 49 Securing Switch Ports • You can choose from several degrees of security on a switch – First, you can configure a permanent MAC address for a specific port on your switch – Second, you could define a static MAC address entry into your switching table • Which maps a restricted communication path between two ports • To configure port security, you first must enter the interface configuration mode
• 50.
  CCNA Guide toCisco Networking Fundamentals 50 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 violation • To turn switchport security off, use: – Rm410HL(config-if)#no switchport port- security • To clear the settings to include erasing the static MAC addresses, use the clear command: – Rm410HL(config-if)#clear port-security
• 51.
  CCNA Guide toCisco Networking Fundamentals 51 Summary • Ethernet (CSMA/CD) is a media access method that was developed in the 1960s • Stations on an Ethernet LAN must listen to the network media before transmitting to ensure that no other station is currently transmitting • If two stations transmit simultaneously on the same collision domain, a collision will occur • The transmitting stations must be able to recognize the collision and ensure that other stations know about it by transmitting a jam signal
• 52.
  CCNA Guide toCisco Networking Fundamentals 52 Summary (continued) • The delays caused by collisions on a network can seriously affect performance when collisions exceed 5% of the traffic on the collision domain • Switches do the most to divide the collision domain and reduce traffic without dividing the broadcast domain • A switch microsegments unicast traffic • Another way to increase the speed at which a LAN operates is to upgrade from Ethernet to Fast Ethernet • Full duplex can also improve Ethernet performance
• 53.
  CCNA Guide toCisco Networking Fundamentals 53 Summary (continued) • Full duplex allows frames to be sent and received simultaneously • As with Fast Ethernet, full-duplex operations are only supported by devices designed for this type of communication • The two types of operating systems on Cisco switches are IOS-based and set-based • Configuring a switch is similar to configuring a router through the CLI • Switches can provide some level of security through the use of port security commands