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