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Network+ Guide to Networks

Network+ Guide to Networks. Review. NICs (Network Interface Cards). Connectivity devices Enable device transmission Transceiver - Transmits and receives data Physical layer and Data Link layer functions

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Network+ Guide to Networks

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  1. Network+ Guide to Networks Review

  2. NICs (Network Interface Cards) • Connectivity devices • Enable device transmission • Transceiver - Transmits and receives data • Physical layer and Data Link layer functions • Issue data signals; Assemble and disassemble data frames; Interpret physical addressing information; Determine right to transmit data • Common to every networking device, network

  3. Repeater • Repeater • Simplest connectivity device regenerating signals • Operates at Physical layer • Has no means to interpret data • Limited scope • One input port, one output port • Receives and repeats single data stream • Suitable for bus topology networks • Extends network inexpensively • Rarely used on modern networks • Limitations; other devices decreasing costs

  4. Stand-alone hub Hub • Hub • Repeater with more than one output port • Multiple data ports, uplink port • Repeats signal in broadcast fashion • Operates at Physical layer • Ethernet network hub • Star or star-based hybrid central connection point • Connect workstations, print servers, switches, file servers, other devices • Devices share same bandwidth amount, collision domain • More nodes leads to transmission errors, slow performance

  5. Bridges • Connects two network segments • Analyze incoming frames and decide where to send • Based on frame’s MAC address • Operate at Data Link layer • Single input port and single output port • Interpret physical addressing information • Advantages over repeaters and hubs • Protocol independence (can be used with non-routable protocols) • Add length beyond maximum segments limits • Improve network performance • Disadvantage compared to repeaters and hubs • Longer to transmit data

  6. Bridges • Filtering database (forwarding table) • Used in decision making - Filter or forward • Forwards packets in following manner: If source and destination addresses are located on the same segment, packet will not be forwarded across the bridge to another segment If destination address of packet is not in bridge’s table, bridge forwards packets to all of its nodes, possibly creating broadcast storms • Today bridges nearly extinct • Improved router and switch speed, functionality • Lowered router and switch cost

  7. Switches Switches • Subdivide network • Smaller logical pieces, segments • Operates at Data Link layer (traditional) • Operate at OSI layers 3 and 4 (advanced) • Interpret MAC address information • Components • Internal processor, operating system, memory, several ports • Multiport switch advantages over bridge • Better bandwidth use, more cost-efficient • Each port acts like a bridge • Each device effectively receives own dedicated channel • Ethernet perspective • Dedicated channel represents collision domain

  8. Routers • Multiport connectivity device • Directs data between network nodes • Integrates LANs and WANs • Different transmission speeds, protocols • Operate at Network layer (Layer 3) • Directs data from one segment or network to another • Logical addressing (network/IP) • Protocol dependent • Slower than switches and bridges • Need to interpret Layers 3 and higher information

  9. Placement of routers on a LAN Router Characteristics and Functions • Directing network data • Static routing • Administrator programs specific paths between nodes • Dynamic routing • Router automatically calculates best path between two nodes

  10. Distance-Vector: RIP, RIPv2, BGP • Distance-vector routing protocols • Determine best route based on distance to destination • Factors • Hops, latency, network traffic conditions • RIP (Routing Information Protocol) • Only factors in number of hops between nodes • Limits 15 hops • Interior routing protocol • Slow and less secure • BGP • Routing protocol used on Internet backbones

  11. Link-State: OSPF, IS-IS • Link-state routing protocol • Routers share information • Each router independently maps network, determines best path • OSPF (Open Shortest Path First) • Interior or border router use • No hop limit • Complex algorithm for determining best paths • Each OSPF router • Maintains database containing other routers’ links

  12. Gateways and other Multifunction Devices • Gateway • Combinations of networking hardware and software • Connecting two dissimilar networks • Connect two systems using different formatting, communications protocols, architecture • Repackages information • Reside on servers, microcomputers, connectivity devices, mainframes • Popular gateways • E-mail gateway, Internet gateway, LAN gateway, Voice/data gateway, Firewall

  13. Figure 7-1 Differences in LAN and WAN connectivity WAN Topologies • Differences from LAN topologies • Distance covered, number of users, distance traveled • Connect sites via dedicated, high-speed links • Use different connectivity devices • WAN connections • Require Layer 3 devices • Routers • Not capable of nonroutable protocols

  14. Figure 7-2 A bus topology WAN Bus • Each site connects to two sites maximum serially • Similar LAN topology site dependency • Network site dependent on every other site to transmit and receive traffic • Difference from LAN topology • Different locations connected to another through point-to-point links • Best use • Organizations requiring small WAN, dedicated circuits • Drawback • Not scalable

  15. Figure 7-3 A ring topology WAN Ring • Each site connected to two other sites • Forms ring pattern • Similar to LAN ring topology • Differences from LAN ring topology • Connects locations • Relies on redundant rings • Data rerouted upon site failure • Expansion • Difficult, expensive • Best use • Connecting 4, 5 locationsmaximum

  16. Figure 7-4 A star topology WAN Star • Mimics star topology LAN • Single site central connection point • Separate data routes between any two sites • Advantages • Single connection failure affects one location • Different from bus, star topology • Shorter data paths between any two sites • When all dedicated circuits functioning • Expansion: simple, less costly • Drawback • Central site failure

  17. Figure 7-5 Full-mesh and partial-mesh WANs Mesh • Incorporates many directly interconnected sites • Data travels directly from origin to destination • Routers can redirect data easily, quickly • Most fault-tolerant WAN type • Full-mesh WAN • Every WAN site directly connected to every other site • Drawback: cost • Partial-mesh WAN • Reduce costs

  18. X.25 and Frame Relay • X.25 ITU standard • Analog, packet-switching technology • Designed for long distance • Original standard: mid 1970s • Mainframe to remote computers: 64 Kbps throughput • Update: 1992 • 2.048 Mbps throughput • Client, servers over WANs • Verifies transmission at every node • Excellent flow control, ensures data reliability • X.25: errors fixed or retransmitted; slow • 64 Kbps to 45 Mbps

  19. X.25 and Frame Relay (cont’d.) • Frame relay • Updated X.25: digital, packet-switching • Protocols operate at Data Link layer • Supports multiple Network, Transport layer protocols • No reliable data delivery guarantee • Customer chooses throughput • Both use virtual circuits • Based on potentially disparate physical links • Logically appear direct • Advantage: efficient bandwidth use • Both configurable as SVCs (switched virtual circuits) or PVCs (permanent virtual circuits) • SVC - Connection established for transmission, terminated when complete • PVC - Connection established before transmission, remains after transmission

  20. ISDN • Digital data transmitted over PSTN • Gained popularity: 1990s • Connecting WAN locations • Exchanges data, voice signals • Protocols at Physical, Data Link, Transport layers • Signaling, framing, connection setup and termination, routing, flow control, error detection and correction • Relies on PSTN for transmission medium • Dial-up or dedicated connections • Dial-up relies exclusively on digital transmission

  21. ISDN (cont’d.) • Single line • Simultaneously: two voice calls, one data connection • Two channel types • B channel: “bearer” • Circuit switching for voice, video, audio: 64 Kbps • D channel: “data” • Packet-switching for call information: 16 or 64 Kbps • BRI (Basic Rate Interface) connection • 2 B channels and 1 D channel • PRI (Primary Rate Interface) connection • 23 B channels and 1 D channel

  22. T-Carriers • T1s, fractional T1s, T3s • Physical layer operation • Single channel divided into multiple channels • Using TDM (time division multiplexing) over two wire pairs • Medium • Telephone wire, fiber-optic cable, wireless links • Wiring • Plain telephone wire • UTP or STP copper wiring • STP preferred for clean connection • Coaxial cable, microwave, fiber-optic cable • T1s using STP require repeater every 6000 feet • Multiple T1s • Coaxial cable, microwave, fiber-optic cabling • T3s require microwave, fiber-optic cabling

  23. Table 7-1 Carrier specifications – most common T1 and T3 Types of T-Carriers (cont’d.) • T1 use • Connects branch offices, connects to carrier • Connects telephone company COs, ISPs • T3 use • Data-intensive businesses • T3 provides 28 times more throughput (expensive) • Multiple T1’s may accommodate needs • TI costs vary by region • Fractional T1 lease • Use some T1 channels, charged accordingly

  24. Figure 7-13 A CSU/DSU T-Carrier Connectivity (cont’d.) • CSU/DSU (Channel Service Unit/Data Service Unit) • Two separate devices • Combined into single stand-alone device • Interface card • T1 line connection point • At customer’s site • CSU • Provides digital signal termination • Ensures connection integrity • DSU • Converts T-carrier frames into frames LAN can interpret (vice versa) • Connects T-carrier lines with terminating equipment • Incorporates multiplexer

  25. Figure 7-14 A point-to-point T-carrier connection T-Carrier Connectivity (cont’d.) • Incoming T-carrier line • Multiplexer separates combined channels • Outgoing T-carrier line • Multiplexer combines multiple LAN signals

  26. T-Carrier Connectivity (cont’d.) • Terminal Equipment • Switches, routers, bridges • Best option: router, Layer 3 or higher switch • Accepts incoming CSU/DSU signals • Translates Network layer protocols • Directs data to destination • CSU/DSU may be integrated with router, switch • Expansion card • Faster signal processing, better performance • Less expensive, lower maintenance solution

  27. DSL • DSL (digital subscriber line) • Operates over PSTN • Directly competes with ISDN, T1 services • Requires repeaters for longer distances • Best suited for WAN local loop • Supports multiple data, voice channels • Over single line • Higher, inaudible telephone line frequencies • Uses advanced data modulation techniques • Data signal alters carrier signal properties • Amplitude or phase modulation

  28. Types of DSL • xDSL refers to all DSL varieties • ADSL, G.Lite, HDSL, SDSL, VDSL, SHDSL • Two DSL categories • Asymmetrical and symmetrical • Downstream • Data travels from carrier’s switching facility to customer • Upstream • Data travels from customer to carrier’s switching facility • Downstream, upstream throughput rates may differ • Asymmetrical • More throughput in one direction • Downstream throughput higher than upstream throughput • Best use: video conferencing, web surfing • Symmetrical • Equal capacity for upstream, downstream data • Examples : HDSL, SDSL, SHDSL • Best use: uploading, downloading significant data amounts

  29. Table 7-2 Comparison of DSL types Types of DSL (cont’d.) • How DSL types vary • Data modulation techniques • Capacity • Distance limitations • Not available in all areas of the U.S. either because carriers have not upgraded their switching equipment or customers do not reside within the service’s distance limitations • PSTN use

  30. Figure 7-17 A DSL connection DSL Connectivity • ADSL: common example on home computer • Establish TCP connection • Transmit through DSL modem • Internal or external • Splitter separates incoming voice, data signals • May connect to hub, switch, router • DSL competition • T1, ISDN, broadband cable • DSL installation • Hardware, monthly access costs • Slightly less than ISDN, significantly less than T1s • DSL drawbacks • Not available in all areas • Upstream throughput lower than broadband cable • Consumers use broadband Internet access service

  31. Figure 7-18 A cable modem Broadband Cable • Cable companies connectivity option • Based on TV signals coaxial cable wiring • Theoretically transmission • 150 Mbps downstream, 10 Mbps upstream • Real transmission • 10 Mbps downstream, 2 Mbps upstream • Transmission limited ( throttled) • Shared physical connections • Best use • Web surfing • Network data download

  32. Figure 7-19 Cable infrastructure Broadband Cable (cont’d.) • Requires cable modem • Modulates, demodulates transmission, reception signals via cable wiring • Operates at Physical and Data Link layer • May connect to connectivity device • Provides dedicated connection • Many subscribers share same local line, throughput • The greater the number of userssharing a single line, the lessthroughput available to eachindividual user

  33. ATM (Asynchronous Transfer Mode) • Functions in Data Link layer • Asynchronous communications method • Nodes do not conform to predetermined schemes • Specifying data transmissions timing • Each character transmitted • Start and stop bits • Specifies Data Link layer framing techniques • Fixed packet size • Sets ATM apart from Ethernet • Packet (cell) • 48 data bytes plus 5-byte header • Smaller packet size requires more overhead • Decrease potential throughput • Cell efficiency compensates for loss

  34. ATM (cont’d.) • ATM relies on virtual circuits • ATM considered packet-switching technology • Virtual circuits provide circuit switching advantage • Reliably available point-to-point connection • Reliable connection • Allows specific QoS (quality of service) guarantee • Important for time-sensitive applications • Compatibility • Other leading network technologies • Cells support multiple higher-layer protocol • LANE (LAN Emulation) • Allows integration with Ethernet, token ring network • encapsulates incoming Ethernet or token ring frames • Converts to ATM cells for transmission • Throughput • 25 Mbps to 622 Mbps • Cost • Relatively expensive

  35. SONET (Synchronous Optical Network) • Four key strengths • WAN technology integration • Fast data transfer rates • Simple link additions, removals • High degree of fault tolerance • Synchronous • Data transmitted, received by nodes conforms to timing scheme • Advantage • Interoperability • Fault tolerance • Double-ring topology over fiber-optic cable

  36. SONET (cont’d.) • SONET Ring • Begins, ends at telecommunications carrier’s facility • Connects organization’s multiple WAN sites in ring fashion • Connect with multiple carrier facilities • Additional fault tolerance • Terminates at multiplexer • Easy SONET ring connection additions, removals

  37. Table 7-3 SONET OC levels SONET (cont’d.) • Implementation • Large companies • Long-distance companies • Linking metropolitan areas and countries • ISPs • Guarantying fast, reliable Internet access • Telephone companies • Connecting Cos • COST • Expensive

  38. WAN Technologies Compared

  39. Remote Connectivity • Remote access • Service allowing client connection, log on capability • LAN or WAN in different geographical location • Remote client • Access files, applications, shared resources • Remote access communication requirement • Client, host transmission path • Appropriate software • Dial-up networking, Microsoft’s RAS or RRAS, VPNs

  40. Dial-Up Networking • Dialing directly into private network’s or ISP’s remote access server • Log on to network • Transmission methods • PSTN, X.25, ISDN • Advantages • Technology well understood • Software availability • Disadvantages • Throughput • Quality • Administrative maintenance • Microsoft software • RAS (Remote Access Service) • RRAS (Routing and Remote Access Service)

  41. Remote Access Servers • Server requirements • Accept client connection • Grant privileges to network’s resources • Device types • Dedicated devices: Cisco’s AS5800 access servers • Computers installed with special software • Microsoft remote access software • RRAS (Routing and Remote Access Service) • Computer accepts multiple remote client connections • Server acts as router • Multiple security provisions

  42. Remote Access Protocols • SLIP and PPP • Workstations connect using serial connection • Encapsulate higher-layer networking protocols, in lower-layer data frames • SLIP carries IP packets only • Harder to set up • Supports only asynchronous data • PPP carries many different Network layer packets • Automatic set up • Performs error correction, data compression,supports encryption • Supports asynchronous and synchronous transmission • PPPoE (PPP over Ethernet) standard • Used over an Ethernet network (no matter what the connection type) • Connects home computers to ISP • Via DSL, broadband cable

  43. Remote Virtual Computing (cont’d.) • Remote desktop • Windows client and server operating systems • Relies on RDP (Remote Desktop Protocol) • Application layer protocol • Uses TCP/IP to transmit graphics, text quickly • Carries session, licensing, encryption information • Exists for other operating systems • Not included in Windows home editions

  44. VPNs (Virtual Private Networks) • Wide area networks • Logically defined over public transmission systems • Type of network that allows organization to carve out a private WAN through the Internet, serving only its offices, while keeping the data secure and isolated from other public network • Software • Inexpensive; Sometimes included with other widely used software • Tailored to customer’s distance, bandwidth needs • Two important design considerations • Interoperability and security • PPTP (Point-to-Point Tunneling Protocol) • Microsoft - Encryption, authentication, access services • Dial directly into RRAS access server • Dial into ISP’s remote access server first • L2TP (Layer 2 Tunneling Protocol) • Cisco • Connects VPN using equipment mix • Connect two routers • Tunnel endpoints not on same packet-switched network

  45. What Are Integrity and Availability? • Integrity • Network’s programs, data, services, devices, connections soundness • Availability • How consistently, reliably a file or system can be accessed • By authorized personnel • Both are compromised by: • Security • Breaches, natural disasters, malicious intruders, power flaws, human error • User error • Unintentional • Harm data, applications, software configurations, hardware • Intentional • Administrators must take precautionary measures to protect network • Cannot predict every vulnerability • Follow general guidelines for protecting network

  46. Malware • Program or code • Designed to intrude upon or harm system and resources • Examples: viruses, Trojan horses, worms, bots • Virus • Replicating program intent to infect more computers • Through network connections, exchange of external storage devices • Many destructive programs often called viruses • Do not meet strict criteria of virus • Example: Trojan horse • Categories based on location and propagation • P. 687 in textbook – look at definitions • Boot sector viruses • Macro Virus • File-infector virus • Worm • Trojan horse • Network Virus • Bot

  47. Malware Characteristics • Making malware harder to detect and eliminate • Encryption • Used by viruses, worms, Trojan horses • Thwart antivirus program’s attempts to detect it • Stealth • Malware hides itself to prevent detection • Disguise themselves as legitimate programs, code • Polymorphism • Change characteristics every time they transfer to new system • Use complicated algorithms, incorporate nonsensical commands • Time dependence • Programmed to activate on particular date • Can remain dormant, harmless until date arrives • Logic bombs: programs designed to start when certain conditions met • Malware can exhibit more than one characteristic

  48. Malware Protection • Not just installing any virus-scanning program or anti-malware software • Requires: • Choosing appropriate anti-malware program • Monitoring network • Continually updating anti-malware program • Educating users

  49. Anti-Malware Software • Malware leaves evidence • Some detectable only by anti-malware software • User viewable symptoms • Unexplained file size increases • Significant, unexplained system performance decline • Unusual error messages • Significant, unexpected system memory loss • Periodic, unexpected rebooting • Display quality fluctuations • Malware often discovered after damage done • Minimal anti-malware functions • Detect malware through signature scanning • Comparing file’s content with known malware signatures • Detect malware through integrity checking • Comparing current file characteristics against archived version • Detect malware by monitoring unexpected file changes • Receive regular updates and modifications • Consistently report only valid instances of malware • Heuristic scanning: identifying malware by discovering “malware-like” behavior • Anti-malware software implementation • Dependent upon environment’s needs • Key: deciding where to install software

  50. Anti-Malware Policies • Malware prevention • Apply technology, forethought • Policies provide rules for: • Using anti-malware software • Installing programs, sharing files, using external disks • Management should authorize and support policy • Anti-malware policy guidelines • Protect network from damage, downtime

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