Switches- Chapter 2

1. Switches- Chapter 2 CCNA Exploration Semester 3 Modified by Profs. Ward and Cappellino

2. Topics • Operation of 100/1000 Mbps Ethernet • Switches and how they forward frames • Configure a switch • Basic security on a switch

3. LAN Design Basic Switch Concepts- Chp. 2 Wireless VLANs STP Inter-VLAN routing VTP LAN Switching and Wireless

4. CSMA/CD reminder • Shared medium-Physical sharedcable or hub. • Ethernet wasdesigned to work________________ • Using _________________________________ ____________________________

5. CSMA/CD review… • Device needs to transmit. • It “__________” for signals on the medium. • If it finds signals – ______. If clear – __________. • If the signals of one device are not detected by a second device, the second device may also start to transmit causing a ____________________. • Stop sending frame, send ____________ • Wait for random time (_____________) • ______________ – listen for signals etc.

6. No collisions • ______________________ with _________ operation = __________ collisions. • Higher bandwidth Ethernet does not define collisions – must be fully switched. • Cable length limited if CSMA/CD needed. • ________ – always fully switched, full duplex. • (Shared medium must use half duplex in order to detect collisions.)

7. Switch Port Settings • Auto (default for UTP) - ____________________ with connected device. • Two ports communicate to decide the best mode of operation • Full – sets full-duplex mode • Half - sets half-duplex mode • Auto is fine if _______ types of devices are using it. • Potential problem- if switch uses auto and other device does not. Switch defaults to half. • Manually setting full-duplex on one end and half on the other __________________________

8. MDIX autoInterface config command • _________________ whether cable is straight through or crossover and configures the interface accordingly • Either cable type can be used in the connection • Depends on IOS version • Enabled by default from 12.2(18)SE or later • Disabled from 12.1(14)EA1 to 12.2(18)SE • _________________ in earlier versions EXAMPLE… Switch# configure terminal Switch(config)# interface gigabitethernet0/1 Switch(config-if)# speed auto Switch(config-if)# duplex auto Switch(config-if)# mdix auto Switch(config-if)# end

9. Communication types review… • _________ – one sender to one receiver • most user traffic: http, ftp, smtp etc. • ________________ – one sender, but the information is sent to all connected receivers. • Ex: ARP requests • ___________ – a frame is sent from one sender to a specific group of devices • Ex: Group of hosts using videoconferencing. • IP addresses have first octet in range 224 – 239

10. Ethernet frame review… • 802.2 is data link layer LLC sublayer

11. MAC address review… • ___________written as _________ hexadecimal digits. Format varies: 00-05-9A-3C-78-00, 00:05:9A:3C:78:00, or 0005.9A3C.7800. • MAC address __________________ into a ROM chip on a NIC • Referred to as a burned in address (BIA). • Some manufacturers allow the MAC address to be _________________. • What is the purpose of MAC address?

12. On the destination MAC address, bit is set if frame’s address is a ____________________ MAC address review… • Two parts: Organizational Unique Identifier (___) and number _____________________

13. MAC address • Two parts: Organizational Unique Identifier (OUI) and number assigned by manufacturer. Set if vendor assigned MAC address can be ____________________

14. MAC address • Two parts: Organizational Unique Identifier (OUI) and number assigned by manufacturer. Assigned to vendor by ________

15. MAC address • Two parts: Organizational Unique Identifier (OUI) and number assigned by manufacturer. _______________ for the Ethernet device

16. Switch MAC Address Table review… • Table created by mapping the switch port to MAC address of attached device • Built by inspecting _____________ address of incoming frames • ________________ address checked against table • Frame sent through correct port • If not in table, frame __________________ on which it was received • Broadcasts flooded

17. Bandwidth and Throughput review.. • What is Bandwidth? • What is Throughput? • Bandwidth is affected by _____________ • Full bandwidth for transmission is available only after any collisions have been resolved. • Number of nodes sharing the Ethernet network will have effect on the ___________

18. Collision domain review… • Collision Domain-- __________________________ ___________________________________ • Collisions ___________ throughput • Shared medium – same collision domain • The more devices – the more collisions • Hub – an average of 60% of bandwidth available • Switch (+ full duplex) • Microsegmentation- connection created by ________ between sending and receiving hosts • Full duplex- dedicated link each way • 100% bandwidth in each direction • Link regarded as an individual collision domain if you are asked to count them.

19. How many collision domains?

20. Broadcast domain review… • Layer 2 switches ________________ broadcasts • Do not filter broadcast frames • Devices linked by switches are ______________ broadcast domain. • We ignore VLANs here – they come later • A _______________________, splits up broadcast domains • Does not forward broadcasts • Destination MAC address for broadcast is all 1s, that is FF:FF:FF:FF:FF:FF

21. How many broadcast domains? No VLANs

22. Network Latency • Latency- ____________________ from the source to the final destination • Three sources: • ___________ – time taken to put signal on medium and to interpret it on receipt. • ____________________ – time spent travelling on medium • Latency from _______________________ • These are either Layer 1, 2, or 3 devices • Depends on number and type of devices. • Routers add more latency than switches.

23. Network congestion • Common causes of congestion: • More powerful PCs that can send and process more data through the network at higher rates. • Increasing use of remote resources (servers, Internet) generates more traffic volume. • More broadcasts, more congestion. • High-bandwidth applications make more use of advanced graphics, video etc. • Need more bandwidth. • ________________________________ helps.

24. Control latency • Choose switches that can process data fast enough for all ports to work simultaneously at full bandwidth. • Switches that lack sufficient processing power can introduce latency • Use _______________ rather than ________ where possible. • Routers increase latency on a network • But – balance this against need to split up broadcast domains • Which is done by routers

25. Remove bottlenecks • Bottlenecks- places on the network where _____________________________________ • Reduce bottlenecks by having several links • Use _______________ so they act as one link with the combined bandwidth. • Use higher capacity links

26. Switch Forwarding Methods • Current models of Cisco switches now use only __________________________ of switching data between ports • Some older switches used Cut Through – it had two variants: Fast Forward and Fragment Free

27. Store and forward • _____________________________ • Discard any frames that are too short/long • Perform cyclic redundancy check (CRC) and ___________________________ • Find correct port and forward frame out that port • Required for ______________ checks on converged networks • Allows entry and exit at _________________

28. Cut Through - Fast forward • Read _____________________, through to the ____________________________ (first 6 bytes after start delimiter) • Look up port and ______________ while _______________ of frame is still _____________ • No error checking or discarding of bad frames • Entry and exit must be same bandwidth • ________________________ • Corrupt frames could be sent throughout the network

29. Cut Through – Fragment Free • ________________________________________________________________________________ • Look up port and start forwarding while remainder of frame (if any) is still coming in. • Most network errors and collisions occur during the first 64 bytes. • Discards collision fragments (too short) but other bad frames are forwarded • Entry and exit must be ________________ • Compromise between Store and forward and Fast forward methods

30. Symmetric and Asymmetric Switching • ______________ – all ports operate at ___________ bandwidth • __________ – __________ bandwidths may be used • Ex: greater bandwidth dedicated to a server or uplink port to prevent bottlenecks • Requires store and forward operation with memory buffering • Most switches now use _____________ switching to allow ________________

31. Port Based Buffering • Each incoming port has ________________ • Frames ________________ until _________port is free. • Frame destined for busy outgoing port can hold up all the frames in queue even if their outgoing ports are free. • Each incoming port has a ______________ amount of memory.

32. Shared Memory Buffering • All incoming frames go in a __________ ___________________________________ • Switch __________________________ and forwards it when port is free • Frames do not hold each other up • Flexible use of memory allows larger frames • Important for asymmetric switching where some ports work at a faster rate than others

33. Layer 2 and Layer 3 Switching Traditional Ethernet switches work at ______ They use ___________ ___________to make filtering and forwarding decisions. They do not look at layer 3 information.

34. Layer 2 and Layer 3 Switching ______________ can carry out the same functions as layer 2 switches. They can also use ___________________ ___________ between networks. The can control the spread of broadcasts.

35. L 3 Switch & Router Comparison • Routers perform __________________________ • L3 Switches provide _________ routing functions in a LAN and reduce the need for dedicated routers

36. Switch CLI is similar to router • Switch>enable • Switch#config t • Switch(config)#int fa 0/1 • Switch(config-if)#exit • Switch(config)#line con 0 • Switch(config-line)#end • Switch#disable • Switch>

37. Cisco Device manager • ____________________ for managing switch. • Access via browser on PC. • Other GUI options available but need to be downloaded/bought.

38. Help, history etc. • Help with_________is similar to router. • Error messages for bad commands – same as for a router • Command history – same as for router. • Up arrow or Ctrl + P for previous • Down arrow or Ctrl + N for next • Each mode has its own buffer holding 10 commands by default.

39. Storage and start-up • ROM, Flash, NVRAM, RAM generally similar to router. • Boot loader (similar process to router) • Performs low-level _________________ • Performs ____________________________ • During POST, LEDs blink while a series of tests determine that the switch is functioning properly- green is good! • If the switch fails POST, the SYST LED turns amber. • ________________________________ • Loads a ______________ software image into memory and ______________ the switch. • ___________________________________ as found in the config file or alternate location • Boot loader lets you re-install IOS or recover from password loss.

40. IP address • A switch works “out-of-the-box” without an IP address (it’s a L2 device) or any other configuration • IP address lets you access/program the switch remotely by Telnet, SSH or browser. • Switch needs _______________ IP address. • Programmed on an interface within a VLAN • VLAN ________ is the __________ but is not very secure for management so best practices states ______________________________

41. IP address assignment example • First- create a VLAN and assign an IP address… • S1(config)#int vlan 99 ( or another VLAN) • S1(config-if)#ip address 192.168.1.2 255.255.255.0 • S1(config-if)#no shutdown • S1(config-if)#exit

42. IP address assignment example cont… • Second- assign the appropriate port the switch to VLAN 99 … • S1(config)#int fa 0/18 (or other interface) • S1(config-if)#switchport mode access • S1(config-if)#switchport access vlan 99 • S1(config-if)#exit • S1(config)# • Management information to and from the switch can now pass via port fa 0/18. • Other ports could be added to VLAN 99 if necessary.

43. Default gateway • S1(config)#ip default-gateway 192.168.1.1 • Just like a PC, the switch needs to _______ ______________________________ to exchange switch management traffic destinations outside its local network • Note _______________________ mode.

44. Configuring a switch as an HTTP server… • Required by a number of web-based configuration tools available on switches • SW1(config)#ip http server • SW1(config)#ip http authentication enable • (uses enable secret/password for access) • SW1(config)#ip http authentication local • SW1(config)#username admin password cisco • (log in using this username and password)

45. MAC address table (CAM) • What is the MAC address table used for? • Static MAC addresses:Inbuilt or configured, _____________ • Dynamic MAC addresses:Learned, __________________________ • Note that VLAN number is included in table.

46. Set a static MAC addressexample… • SW1(config)#mac-address-table static 000c.7671.10b4 vlan 2 interface fa0/6

47. Save configuration • Copy running-config startup-config • Copy run start- shortened version of command • This assumes that running-config is coming from RAM and startup-config is going in NVRAM (file is actually in flash). • Full (formal) version of command would be: • Copy system:running-config flash:startup-config

48. Back up • ____________________ can be _________ in different _____________ using the following command.. • copy startup-config flash:backupJan08 • You could go back to this version later if necessary. • Backing up to a TFTP server (same process as for a router)… • copy system:running-config tftp://192.168.1.8/sw1config • or try copy run tftp and wait for prompts • copy nvram:startup-config tftp://192.168.1.8/sw1config

49. Restoring • Coping a saved configuration over the current configuration • As with a router, you can swap the copy commands listed previously with the destination being the startup-config • then issue the _____________ command • Could we use the “copy startup-config running-config” command?

50. Login Passwords- Review… • The process of securing and removing passwords is the ______________ for routers and switches. • What are the different password that can be set (on a router and switch) ?