Post on 14-Jan-2016
transcript
Chapter 17
Connecting Devices
AndVirtualLANs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 17: Outline
17.1 17.1 CONNECTING DEVICESCONNECTING DEVICES
17.2 17.2 VIRTUAL LANSVIRTUAL LANS
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17-1 CONNECTING DEVICES17-1 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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17-1 CONNECTING DEVICES17-1 CONNECTING DEVICES
Connecting devices can operate in different layers of the TCP/IP model.
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17-1 CONNECTING DEVICES17-1 CONNECTING DEVICES
three common connecting devices:
repeater-hubs, link-layer switches, and routers.
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Figure 17.1: Three categories of connecting devices
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17.17.1 Repeater-Hubs17.17.1 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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17.17.1 Repeater-Hubs17.17.1 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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Figure 17.2: Hub
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17.17.2 Link-Layer Switches17.17.2 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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17.17.2 Link-Layer Switches17.17.2 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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17.17.2 Link-Layer Switches17.17.2 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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Figure 17.3: Link-Layer Switch
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17.17.2 Link-Layer Switches17.17.2 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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17.17.2 Learning Switch 17.17.2 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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17.17.2 Switch Software17.17.2 Switch Software
SNMP = Switch Network Mapping Protocol Managed Switch Port Mapping Tool NetDB = Network Tracking Database OpUtils Lan-sweeper
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Figure 17.4: Learning switch
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17.17.2 Switchs17.17.2 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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Figure 17.5: Loop problem in a learning switch (Part a)
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Figure 17.5: Loop problem in a learning switch (Part b)
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Figure 17.5: Loop problem in a learning switch (Part c)
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Figure 17.5: Loop problem in a learning switch (part d)
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Figure 17.6: A system of connected LANs and its graph (Part a)
Switch link assignment
Switch to Lan = 1 Lan to Switch = 0
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Figure 17.6: A system of connected LANs and its graph (Part b)
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Figure 17.7: Finding the shortest path and the spanning tree for a switch.
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Figure 17.8: Forwarding and blocking ports after using spanning
tree algorithm
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17.17.3 Routers17.17.3 Routers
We will discuss routers in Part IV of the book when we discuss the network layer.
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17.17.3 Routers17.17.3 Routers
A router is a three-layer device; it operates in the physical, data-link, and network layers.
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Figure 17.9: Routing example
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17-2 VIRTUAL LANS17-2 VIRTUAL LANS
A virtual local area network (VLAN) is a local area network configured by software, not by physical wiring.
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Figure 17.10: A switch connecting three LANs by wire
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Figure 17.11: A switch using VLAN software
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Figure 17.12: Two switches in a backbone using VLAN software
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17.2.1 Membership17.2.1 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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17.2.1 VLAN17.2.1 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