1 / 43

CCNA 3 v4.0 Chapter 2 Basic Switch Concepts and Configuration

CCNA 3 v4.0 Chapter 2 Basic Switch Concepts and Configuration. Overview. Ethernet for 100/1000Mbps LANs in IEEE 802.3 standard Switch functions Switch Configuration in networks for voice, video, and data Basic Security for switches. Ethernet/802.3 LAN Networks.

unity-ball
Télécharger la présentation

CCNA 3 v4.0 Chapter 2 Basic Switch Concepts and Configuration

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CCNA 3 v4.0Chapter 2Basic Switch Conceptsand Configuration

  2. Overview • Ethernet for 100/1000Mbps LANs in IEEE 802.3 standard • Switch functions • Switch Configuration in networks for voice, video, and data • Basic Security for switches

  3. Ethernet/802.3 LAN Networks • Ethernet Access Method: CSMA/CD • CSMA/CD is used with half duplex (not full duplex)‏ • Carrier Sense Multiple Access / Collision Detect • Host checks network if clear to transmit • If network is clear, any host can transmit • While transmitting, host also checks if anyone else transmits → giving collision • Detected by increase in amplitude above normal level • When collision detected, jam signal is sent • All hosts then backoff (stop transmitting) for random time • Collisions negatively affects network operation

  4. Ethernet Communications • Three types of communications in switched LAN • Unicast, broadcast, and multicast.

  5. Ethernet Frame • Preamble, Start of Frame Delimiter • Synchronization, tells receiver that data is coming • Ethernet uses MAC address • Note: destination MAC address is first • MAC Address: 48 bits • 24 bit OUI, 24 bit vendor number • Length/Type field: defines exact length of data field. • Or can indicate protocol (> 0x0600). • Frame Check Sequence – for error checking

  6. Duplex Setting • Half Duplex • Unidirectional data flow • 50-60% of 10 Mbps BW • Full Duplex • Bidirectional data flow • 100% of of 10 Mbps BW

  7. Switch Port Settings • Duplex settings • Catalyst switch port can be set for: auto, full, or half • auto-MDIX • Automatic medium-dependent interface crossover • Switch detects cable type for copper Ethernet connections and configures the interfaces accordingly • Can use crossover or straight thru cables • Default on switches running Cisco IOS Release 12.2(18)SE or later

  8. Microsegment, virtual connection between source and destination Switch MAC Address Table • Switch (Layer 2) filters by destination MAC address • Monitors frames • Builds switching table from source MAC address and interface • Switching table in CAM • Destination MAC known • Forwards to that interface! • If destination MAC unknown • Floods out all other interfaces

  9. Collision Domains • Network area where frames originate and collide • Switches create virtual circuit between devices • Dedicated path → smaller collision domain • Microsegmentation – collision-free environment • Maximum utilization of available bandwidth • Each port of a switch is its own collision domain • Switches reduce collisions and improve bandwidth use

  10. Broadcast Domains • Switches forward all broadcasts • Forwards broadcast frame to all ports except incoming port • Collection of interconnected switches is single broadcast domain

  11. Network Latency (delay)‏ • Latency • Time for frame to travel from source to destination • NIC delay • Time for signals to be sent by NIC (source)‏ • Time for signal to be interpreted by NIC (destination)‏ • Standard Ethernet: 10 Mbps → 100 ns per bit • Propagation delay • Time for signal to travel across media • Device latency • Time for device to process signal • Time signal enters device till it leaves device • latencyrouter > latencybridge > latencyswitch > latencyhub

  12. Network Latency (delay)‏ • Switches support high transmission rates of voice, video, and data networks by using ASICs, application-specific integrated circuits • Provide hardware support for many networking tasks • Additional switch features help to reduce network latency • Switching modes, port-based memory buffering, port level QoS, and congestion management

  13. Controlling Network Latency • Switches, when oversubscribed, can introduce latency • Note: full wirespeed per port is typical of core-level switches, not of access-level switches • Bottlenecks - places where high network congestion results in slow performance

  14. Network Congestion • Congestion - traffic in excess of network capacity • Most common causes of network congestion • Increasingly powerful computer & network technologies • Can send more data at higher rates. • Increasing volume of network traffic • High-bandwidth applications. • Desktop publishing, engineering design, video on demand (VoD), electronic learning (e-learning), and streaming video • To relieve congestion • Segment network for greater BW per user

  15. LAN Segmentation • Dividing network into smaller pieces or segments • Fewer users per segment (more BW per user)‏ • Smaller collision domain (isolates traffic)‏ • Reduces congestion - better network performance • Can segment with • Switches • Smaller collision domains • Routers • Smaller collision and broadcast domains

  16. Segmentation with Routers • Routers connects networks and subnetworks • Routers do not forward broadcasts • Each router port (segment) is its own broadcast and collision domain

  17. Segmentation with Switches • Switches segment LANs into microsegments • Smaller collision domain; full BW available • Dedicated, collision-free virtual connection between source and destination

  18. Switching Methods • Two general switching modes used in switches • Store and Forward • Entire frame is received before forwarding • Highest latency but better error detection • Cut-through • Frame forwarded before entire frame is received • Fast-forward • Frame forwarded after destination address is read • Lowest latency but poor error detection • Fragment-free • Checks first 64 bytes (collision window) before forwarding • Filters our collision fragments

  19. Symmetric vs. Asymmetric Switching • Symmetric switching • Between devices with same BW • Asymmetric switching • Between devices of unlike BW • Requires memory buffering • Optimizes client-server traffic, preventing bottleneck at server port

  20. Memory Buffering • Asymmetric switching requires buffering • Two methods to store data before forwarding • Port-based Memory Buffering • Separate queues for each incoming port • Frames sent only when all frames ahead of it have been sent • Shared Memory Buffering • All frames placed in common memory buffer, single queue • Frames are linked to destination port • Can be transmitted without moving to another queue • Permits larger transmitted frames with fewer dropped frames.

  21. Layer 2 and Layer 3 Switching • Layer 2 switching • Based on MAC address • If destination MAC address is unknown • Flood packet • Layer 3 switching • Based on IP Address • If destination IP is unknown • Packet is dropped • Note: Layer 3 switches use specialized hardware and can route as fast as they can switch

  22. Switch CLI • For security reasons, Cisco IOS separated EXEC sessions into two access levels: • User EXEC • Limited number of basic monitoring commands • Default mode • Identified by the > prompt • Privileged EXEC • Access all device commands • Including configuration and management • Can be password-protected • Identified by the # prompt

  23. CLI Configuration Modes • Global configuration mode is accessed from privileged EXEC • Command: switch# configure terminal • Many configuration modes from global configuration mode

  24. GUI-based Alternatives to CLI • There are a number of graphical management alternatives for managing a Cisco switch • Cisco Network Assistant • CiscoView Application • Cisco Device Manager • SNMP Network Management

  25. CLI Help Feature • Use the question mark (?)‏

  26. CLI Error Messages • Help identify problems when incorrect command is entered.

  27. Command History Buffer • CLI maintains a record of entered commands • Default is last 10 commands • show history • Displays history buffer • terminal no history • Disables history buffer (enabled by default)‏ • terminal history • Enables command history • terminal history sizesize • Change number of commands maintained in history buffer • Up to 256 commands can be maintained

  28. Switch Boot Sequence • After Switch is powered on • Loads boot loader from NVRAM • Low-level CPU initialization • Power-on self-test (POST)‏ • If POST fails, SYST LED turns amber (fatal error)! • Initializes flash file system • Loads default IOS image and boots the switch • IOS then initializes interfaces using the configuration file, config.text, stored in flash memory • Note: Boot loader can be used to recover from system crash

  29. Basic Switch Configuration • Rollover cable from computer to console port on switch, and run HyperTerminal. • Management Interface • IP address to manage switch • Default is interface vlan 1 • Recommend that you change • switch(config)# interface vlan 99 • switch(config-if)# ip address 172.16.99.5 255.255.255.0 • switch(config-if)# no shutdown • Default gateway • switch(config)# ip default-gateway 172.16.99.1

  30. Switch Configuration Example • Vlan 99 is management vlan • Switch is like any other device on the vlan 99 subnet

  31. Configuring Speed and Duplex • Default settings: speedauto and duplex auto • Interfaces will negotiate these settings • Can manually configure on interface • speed [ 10 | 100 | auto ] • duplex [ auto | full | half ] • Can have compatibility issues with inter-vendor autonegotiation

  32. Configuring Web Interface • Web interface can be enabled • Sw1(config)# ip http server • Allow browser to access switch for configuration • Can configure authentication to control web access • ip http authentication {aaa | enable | local | tacacs}

  33. Managing MAC address table • Switches learn MAC addresses by noting source MAC address and interface of received frames • Stored in MAC address table (in CAM)‏ • Entries aged out after 300 s (5 min)‏ • Display with: show mac-address-table • Clear table: clear mac-address-table dynamic

  34. Configuring Static MAC addresses • MAC address can be permanently assigned to interface • Enhanced security: only specific device on port • Will not be aged out • Global configuration mode • mac-address-table static <mac-addr> vlanno.int fa <int_no.>

  35. Switch Show Commands

  36. Backup Configs • Can backup configuration to NVRAM or TFTP server • Use copy command to backup configurations • copy running-config startup-config • Backs up current config to NVRAM in startup-config file. • copy startup-config flash:filename • Save the backup config in flash to a different filename. • If you want to save multiple configs. • copy running-config tftp:[[[//location]/directory] /filename] • Backs up current config to TFTP server.

  37. Restore Configs • Use copy command to restore configs. • copy startup-config running-config • copy flash:filenamestartup-config • Restores the config from NVRAM or flash. • Need to do a reload. • copy tftp:[[[//location]/directory] /filename] system:running-config • Restores config from tftp server to running-config. • copy tftp:[[[//location]/directory] /filename] nvram:startup-config • Restores config from tftp server to startup-config file in nvram.

  38. Configuring Port Security • To prevents unauthorized users access on switch port • Limit number of addresses allowed on interface • Specify action to be taken • Port security only on access ports

  39. Configuring Port Security • Port Security Configuration • switchport port-securitymac-address sticky • Sticky address learned dynamically and added to config • To enable port that is err-disabled due to violation: • shutdown, then no shutdown

  40. Configuring Port Security (3)‏ • show port security - to verify port security status

  41. Summary • Switches and Bridges are layer 2 devices • Builds tables from source MAC addresses • Forwards frames out to specific port • Ethernet Networks • Half-duplex vs. Full-duplex • CSMA/CD • Segmentation • Bridges, Switches, or Routers • Smaller collision domain, better performance • Router segments collision and broadcast domains

  42. Summary • Switch operation • Microsegmentation • Filters by MAC address • Modes: store-and-forward, and cut-through • Fast-forward and Fragment-free • Adaptive cut-through • Asymmetric vs Symmetric switching • Port-based and Shared memory buffering

  43. The End

More Related