ccna guide to cisco networking
TRANSCRIPT
CCNA Guide to Cisco Networking
Chapter 2: Network Devices
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Objectives
• Explain the uses, advantages, and disadvantages of repeaters
• Explain the uses, advantages, and disadvantages of hubs
• Define wireless access points
• Define network segmentation
• Explain network segmentation using bridges
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Objectives (continued)
• Explain network segmentation using switches
• Explain network segmentation using routers
• Explain network segmentation using brouters and gateways
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Repeaters
• Length of cable used influence the quality of communication
• Attenuation• Repeaters repeat signals
– Clean and boost digital transmission– Analog networks use amplifiers to boost signal
• Repeaters only work with the physical signal– Cannot reformat, resize, or manipulate the data
• Physical layer (layer 1) device
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Repeaters (continued)
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Repeaters (continued)
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Hubs
• Generic connection device– Physical layer
• Connect several networking cables together
• Active hubs (add amplification)– Multiport repeaters
• Passive hubs (no Amplification)
• Hubs and topology (collapses the bus arch.)
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Hubs (continued)
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Advantages And Disadvantages Of Repeaters And Hubs
• Advantages of using repeaters– Extend network physical distance
– Do not seriously affect network performance
– Special repeaters connect different media
• Copper to fiber
• Disadvantages of using repeaters– Cannot connect different network architectures
• Token Ring and Ethernet
– Cannot reduce network traffic
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Advantages And Disadvantages Of Repeaters And Hubs
(continued)
• Disadvantages of using repeaters
• Do not segment the network– Repeat everything without discrimination– Number of repeaters must be limited
• Repeaters are part of a collision domain
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Wireless Access Points
• Wireless local area networks (WLANs)
• Wireless access points provide cell-based areas– Contains radio transceiver– Function like a hub– Bandwidth is shared– May also function as a wireless repeater
• Wireless clients
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Wireless Access Points (continued)
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Network Segmentation
• Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
• Problems occur with too many nodes on the same network segment or collision domain
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Network Segmentation (continued)
• Collision– Back off algorithm– Back off period
• Segmentation– Collisions and retransmissions are reduced– Contention for bandwidth is reduced
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Network Segmentation (continued)
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Bridges
• Operate at the Data Link layer
• Forward or drop frames
• Cannot filter broadcasts
• MAC to segment # table
• A bridge is a smart repeater ,it reads MAC
• A Bridge segments the network
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Bridges (continued)
Example: 1-4Example: 2-5
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Transparent Bridges
• Also called learning bridges
• Build a table of MAC addresses as frames arrive
• Ethernet networks use transparent bridges
• Token Ring networks use source-routing bridges
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Source-Routing Bridges
• Used in Token Ring networks
• Rely of source of the frame transmission
• Sender sends an “Explorer frame”
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Translation Bridges
• Connect networks with different network architecture
• Example:– Token ring connecting to Ethernet
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Advantages And Disadvantages Of Bridges
• Advantages of using a bridge– Extend physical network– Reduce network traffic with minor
segmentation– Creates separate collision domains– Reduce collisions– Connect different architecture
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Advantages And Disadvantages Of Bridges
(continued)
• Disadvantages of using bridges– Slower than repeaters due to filtering– Do not filter broadcasts– More expensive than repeaters
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Switches
• Operate at the Data Link layer• It is a smart hub or a multi-port bridge• Increase network performance• Creates a Virtual circuits between a
source and a destination computer• Micro segmentation (collision domain is
confined between source and destination• “switched bandwidth” is creating Multiple
virtual circuits
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Switches (continued)
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Switches (continued)
• Can be used between two computers to create two collision domains with dedicated bandwidth
• Can be used between two hubs to create two collision domains each with shared bandwidth
• Filter based on MAC addresses
• Build tables in memory
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Switches (continued)
• Advantages of switches– Increase available network bandwidth– Reduced workload, computers only receive
packets intended for them specifically– Increase network performance– Smaller collision domains
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Switches (continued)
• Disadvantages of switches– More expensive than hubs and bridges
(not really)– Difficult to trace network connectivity
problems through a switch– Does not filter broadcast traffic, like a Bridge
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Routers
• Provide filtering and network traffic control
• Used on LANs and WANs
• Connect multiple segments and networks
• Multiple routers create an “internetwork”
• Operate at the Network layer, layer 3
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Routers (continued)
• Create a table to determine how to forward packets
• Filtering and traffic control base on logical addresses
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Advantages And Disadvantages Of Routers
(continued)
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Physical Versus Logical Addresses
• MAC addresses (Layer2)– Data Link layer application– Used by switches, bridges, and routers– Used for directly connected devices
• Logical addresses (Layer3)– Network and transport protocols dictate the format of
the logical network layer address– TCP/IP, IPX/SPX– IP addresses are assigned manually or by software
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Physical Versus Logical Addresses (continued)
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Advantages And Disadvantages Of Routers
• Advantages of routers– Can connect networks of different architecture
• Token Ring to Ethernet
– Choose best path through or to a network– Create smaller collision domains– Create smaller broadcast domains
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Advantages And Disadvantages Of Routers
(continued)• Disadvantages of routers
– Only work with routable protocols– More expensive than hubs, bridges, and
switches (has to be)– Routing table updates consume bandwidth– Increase latency due to a greater degree of
packet filtering and/or analyzing (real problem for VOIP)
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Brouters
• Hybrid device
• Functions as a router for routable protocols
• Functions as a bridge for non-routable protocols
• Operates at Data Link and Network layers
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Gateways
• A gateway is a combination of hardware and software
• Translate between different protocol suites
• Operates on all 7 layers of the OSI model
• Gateways have the most negative on network performance– Latency
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Summary
• Network administrators use devices to control and extend the usable size of a network
• These devices include repeaters, hubs, bridges, switches, routers, brouters, and gateways
• Repeaters work against attenuation by cleaning and repeating signals that they receive on a network
• Repeaters work at the Physical layer of the OSI model
• They cannot connect different network architectures
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Summary (continued)
• Repeaters do not reduce network traffic or segment the network
• A hub ties several networking cables together to create a link between different stations on a network
• An active hub has its own electrical power and acts as a repeater, whereas a passive hub provides no signal regeneration
• Hubs operate at the Physical layer of the OSI model and do not segment the network
• Network segmentation is the process of isolating hosts onto smaller segments to reduce the possibility of collisions
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Summary (continued)
• Bridges and switches are two devices commonly used to segment networks
• Bridges provide network segmentation by examining the MAC address that is sent in the data frame
• Bridges can use transparent bridging or source-route bridging to determine which segment includes a specific physical address
• Bridges operate at the Data Link layer of the OSI model
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Summary (continued)
• Switches increase network performance by reducing the number of frames transmitted to the rest of a network
• They do this by opening a virtual circuit between the source and the destination
• Switches operate at the Data Link layer of the OSI model
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Summary (continued)
• Routers operate at the Network layer of the OSI model and provide filtering and network-traffic control on LANs and WANs
• They can connect multiple segments and networks
• On a TCP/IP network, routers use IP addresses to route packets to the correct network segment
• Routers use information from routing tables to move packets from one network to another
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Summary (continued)
• A brouter is a hybrid device that functions both as a bridge for non-routable protocols and as a router for routable protocols
• Brouters operate at both the Data Link and Network layers
• Gateways are usually a combination of hardware and software and are used to translate between different protocols
• They usually operate at layer 4 and above in the OSI model