1. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-1 Multi-Switch Ethernet LAN Operation

2. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-2 Data Link Using Multiple Switches Original Signal Received Signal Received Signal Received Signal Regenerated Signal Regenerated Signal UTP 62.5/125 Multimode Fiber 100BASE-TX (100 m maximum) Physical Link 100BASE-TX (100 m maximum) Physical Link 1000BASE-SX (220 m maximum) Physical Link Each trunk line along the way has a distance limit

3. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-3 Multiswitch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 E5-BB-47-21-D3-56 Switch 3, Port 6 D5-47-55-C4-B6-9F Switch 3, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 The Situation: A1… Sends to E5… Frame must go through 3 switches along the way (1, 2, and then 3)

4. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-4 Multiswitch Ethernet LAN Switching Table Switch 1 PortStation 2A1-45-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5D5-47-55-C4-B6-9F 5E5-BB-47-21-D3-56 Switch 2 Switch 1 Port 5 on Switch 1 to Port 3 on Switch 2 A1-44-D5-1F-AA-4C Switch 1, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB-47-21-D3-56 Switch 3, Port 6 Host A1…creates a frame addressed to E5… Host A1… sends the frame to Switch 1. The switch accepts the frame coming in Port 2

5. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-5 Multiswitch Ethernet LAN Switching Table Switch 1 PortStation 2A1-45-D5-1F-AA-4C 7B2-CD-13-5B-E4-65 5D5-47-55-C4-B6-9F 5E5-BB-47-21-D3-56 Switch 2 Switch 1 Port 5 on Switch 1 to Port 3 on Switch 2 A1-44-D5-1F-AA-4C Switch 1, Port 2 B2-CD-13-5B-E4-65 Switch 1, Port 7 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 1 Switch 1 looks up the destination MAC address and notes the port number for that address (Port 5) Switch 1 sends the frame out Port 5 Switch 2 is out that port

6. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-6 Multiswitch Ethernet LAN Switch 2 Switch 1 Switch 3 Port 5 on Switch 1 to Port 3 on Switch 2 Port 7 on Switch 2 to Port 4 on Switch 3 Switching Table Switch 2 PortStation 3A1-44-D5-1F-AA-4C 3B2-CD-13-5B-E4-65 7D5-47-55-C4-B6-9F 7E5-BB-47-21-D3-56 On Switch 2 Switch 2 repeats the process Notes that E5 … uses Port 7 Switch 2 sends the frame out Port 7 The frame goes to Switch 3

7. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-7 Multiswitch Ethernet LAN Switch 2 Switch 3 Port 7 on Switch 2 to Port 4 on Switch 3 A1-44-D5-1F-AA-4C Switch 1, Port 2 D5-47-55-C4-B6-9F Switch 3, Port 2 Switching Table Switch 3 PortStation 4A1-44-D5-1F-AA-4C 4B2-CD-13-5B-E4-65 2D5-47-55-C4-B6-9F 6E5-BB-47-21-D3-56 E5-BB-47-21-D3-56 Switch 3, Port 6 On Switch 3 Switch 3 repeats the process Sends the frame out Port 6 This takes the frame to the destination host

8. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-8 Hierarchical Ethernet LAN Ethernet switches must be arranged in a hierarchical topology In a hierarchical LAN, there is only one possible path between any hosts

9. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-9 Single Point of Failure and 802.1D In a hierarchy, If a switch or trunk line fails, there is no backup These backup links are disabled until a breakdown occurs. Then 802.1w Enables them. Fortunately, the 802.1w Rapid Spanning Tree Protocol allows backup links 2

10. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-10 Virtual LAN (VLAN) with Ethernet Switches The Ethernet administrator can set up virtual LANs (VLANs) Only hosts on the same VLAN can communicate This gives security and reduces traffic congestion

11. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-11 Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Network Capacity Momentary Traffic Peak: Congestion and Latency Time Momentary Traffic Peak: Congestion and Latency Momentary traffic peaks usually last only a fraction of a second; They occasionally exceed the network’s capacity. When they do, frames will be delayed, even dropped.

12. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-12 Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Overprovisioned Network Capacity Momentary Peak: No Congestion Time Overprovisioned Traffic Capacity in Ethernet Overprovisioning: Build high capacity than will rarely if ever be exceeded. This wastes capacity. But cheaper than using priority (next)

13. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-13 Handling Momentary Traffic Peaks with Overprovisioning and Priority Traffic Network Capacity Momentary Peak Time Priority in Ethernet High-Priority Traffic Goes Low-Priority Waits Priority: During momentary peaks, give priority to traffic that is intolerant of latency (delay), such as voice. No need to overprovision, but expensive to implement. Ongoing management is very expensive.

14. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-14 Hub versus Switch Operation Today, Switches Dominate in Ethernet –Earlier Ethernet networks used hubs –When a bit came in one port, the hub broadcast the bit out through all other ports –If A is transmitting, B and all other stations have to wait until A finishes transmitting –Otherwise, their signals will collide, and both will be unreadable –Media access control (MAC) prevents this Figure 4-16

15. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-15 Switch Purchasing Considerations Manageability –SNMP Manager controls many managed switches Figure 4-19

16. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-16 Switch Purchasing Considerations Manageability –Polling enables managers to collect data and diagnose problems –Switches can be fixed remotely by changing their configurations

17. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-17 Physical and Electrical Features Physical Size –Switches fit into standard 19-in wide (48-cm wide) equipment racks –Switch heights usually are multiples of 1U (1.75 in or 4.4 cm) 19 inches (48 cm)

18. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-18 Physical and Electrical Features Port Flexibility –Fixed-port switches No flexibility: The number of ports is fixed 1 or 2U tall Most workgroup switches are fixed-port switches

19. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-19 Physical and Electrical Features Port Flexibility –Stackable switches Fixed number of ports 1U or 2U tall High-speed interconnect bus connects stacked switches Ports can be added in increments of as few as 12

20. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-20 Physical and Electrical Features Port Flexibility –Modular switches 1U or 2U tall Contain one or a few slots Each slot module contains 1 to 4 ports Module

21. © 2009 Pearson Education, Inc. Publishing as Prentice Hall4-21 Physical and Electrical Features Port Flexibility –Chassis switches Several U tall Contain several expansion slots Each expansion board contains several slots Most core switches are chassis switches

22. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-22 Physical and Electrical Features Uplink Ports –Normal Ethernet RJ-45 switch ports transmit on Pins 3 and 6 and listen on Pins 1 and 2 If you connect two normal switch ports on different switches via UTP cords, the ports will not be able to communicate A crossover cable solves this problem Normal Switch Port Normal Switch Port On Parent Switch Pins 3 & 6 Pins 1 & 2 Crossover Cable Pins 1 & 2 Pins 3 & 6

23. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-23 Ethernet Security

24. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-24 802.1X Ethernet Port-Based Access Control Client PC is called the supplicant It sends credentials (proof of identity) to the switch The switch is called the network access server The NAS sends the credentials onto a central authentication server Credentials

25. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-25 802.1X Ethernet Port-Based Access Control Authentication server usually is a RADIUS server Authentication server checks credentials against its authentication database Credentials

26. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4-26 4-21: 802.1X Ethernet Port-Based Access Control RADIUS server sends accept or reject message to NAS Switch accepts or rejects the supplicant client Accept/ Reject Accept/ Reject