1. Chapter 17 Connecting Devices And Virtual LANs 17.# 1
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2. Chapter 17: Outline 17.1 CONNECTING DEVICES 17.2 VIRTUAL LANS 17.#

3. CONNECTING DEVICES
Connecting devices are used to connect hosts together to make a network or to connect networks together to make an internet.
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4. CONNECTING DEVICES
Connecting devices can operate in different layers of the TCP/IP model.
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5. three common connecting devices: repeater-hubs,
link-layer switches, and
routers.
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6. Figure 17.1: Three categories of connecting devices
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7. Repeater-Hubs
A repeater-hub is a multiport device that operates only in the physical layer.
Signals carrying information within a network can travel a fixed distance before attenuation endangers the integrity of the data.
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8. Repeater-Hubs
A repeater receives a signal then regenerates and retimes the original bit pattern.
A repeater-hub (hub for short) is a multiport repeater.
The incoming signal is regenerated, retimed and sent through all ports excluding the entry port.
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9. Figure 17.2: Hub
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10. Link-Layer Switches
A link-layer switch operates in both the physical and the data-link layers.
AKA,
2-layer switch
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11. Link-Layer Switches
As a physical-layer device, it regenerates the signal it receives.
As a link-layer device, the link-layer switch can check the MAC addresses (source and destination) contained in the frame.
Some switches operate using virtual circuit identifiers or virtual path identifiers (or both).
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12. Link-Layer Switches
Example (private Ethernet network with a 2-layer switch)
The switch table needs entries for each connected device MAC addresses and the corresponding port number.
MAC address: 48 bits, 12 nibbles, 6 octets.
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13. Figure 17.3: Link-Layer Switch
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14. Link-Layer Switches
Example (private Ethernet network with a 2-layer switch)
A 2-layer switch is much smarter than a repeater(hub). The switch forwards the message through the appropriate port or ports as determined by the frame header fields.
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15. Learning Switch
A learning switch can build a forwarding table by looking at the source address and corresponding port number.
Frames can be broadcast to the unassigned ports (like a hub) until all the ports are assigned. This can be accomplished with Switch Port Mapping Software
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16. 17.17.2 Switch Software SNMP = Switch Network Mapping Protocol
Managed Switch Port Mapping Tool
NetDB = Network Tracking Database
OpUtils
Lan-sweeper
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17. Figure 17.4: Learning switch
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18. Switchs
Unmanaged switches – plug-n-play, without a management interface.
Managed switches – will include a command line interface.
Smart switches
Managed switches
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19. Figure 17.5: Loop problem in a learning switch (Part a)
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20. Figure 17.5: Loop problem in a learning switch (Part b)
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21. Figure 17.5: Loop problem in a learning switch (Part c)
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22. Figure 17.5: Loop problem in a learning switch (part d)
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23. Figure 17.6: A system of connected LANs and its graph (Part a)
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24. Switch link assignment
Switch to Lan = 1
Lan to Switch = 0
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25. Figure 17.6: A system of connected LANs and its graph (Part b)
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26. Figure 17.7: Finding the shortest path and the spanning tree for a switch.
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27. Figure 17. 8: Forwarding and blocking ports after using spanning
Figure 17.8: Forwarding and blocking ports after using spanning tree algorithm
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28. Routers
We will discuss routers in Part IV of the book when we discuss the network layer.
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29. Routers
A router is a three-layer device; it operates in the physical, data-link, and network layers.
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30. Figure 17.9: Routing example
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31. VIRTUAL LANS
A virtual local area network (VLAN) is a local area network configured by software, not by physical wiring.
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32. Figure 17.10: A switch connecting three LANs by wire
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33. Figure 17.11: A switch using VLAN software
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34. Figure 17.12: Two switches in a backbone using VLAN software
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35. 17.2.1 Membership Characteristic used to group stations in a VLAN:
interface numbers,
port numbers,
MAC addresses,
IP addresses,
or a combination of two or more of these.
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36. VLAN
VLANs …
Save time and money because stations can be moved to any VLAN without re-wiring.
Help manage network traffic
Separate LANS for better security management
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