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

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