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Ccna Presentation

  1. 1. © 2003, Cisco Systems, Inc. All rights reserved.
  2. 2. 2
  3. 3. Data NetworksSharing data through the use of floppy disks is not an efficientor cost-effective manner in which to operate businesses.Businesses needed a solution that would successfullyaddress the following three problems:• How to avoid duplication of equipment and resources• How to communicate efficiently• How to set up and manage a networkBusinesses realized that networking technology couldincrease productivity while saving money. 3
  4. 4. Networking DevicesEquipment that connects directly to a network segment isreferred to as a device.These devices are broken up into two classifications.• end-user devices• network devicesEnd-user devices include computers, printers, scanners, andother devices that provide services directly to the user.Network devices include all the devices that connect the end-user devices together to allow them to communicate. 4
  5. 5. Network Interface CardA network interface card (NIC) is a printed circuit boardthat provides network communication capabilities to andfrom a personal computer. Also called a LAN adapter. 5
  6. 6. Networking Device Icons 6
  7. 7. RepeaterA repeater is a network device used to regenerate a signal.Repeaters regenerate analog or digital signals distorted bytransmission loss due to attenuation. A repeater does notperform intelligent routing. 7
  8. 8. HubHubs concentrateconnections. In otherwords, they take a group ofhosts and allow the networkto see them as a single unit.This is donepassively, without any othereffect on the datatransmission.Active hubs not onlyconcentrate hosts, but they 8also regenerate signals.
  9. 9. BridgeBridges convert network transmission data formats as well asperform basic data transmission management. Bridges, asthe name implies, provide connections between LANs. Notonly do bridges connect LANs, but they also perform a checkon the data to determine whether it should cross the bridge ornot. This makes each part of the network more efficient. 9
  10. 10. Workgroup SwitchWorkgroup switches addmore intelligence to datatransfer management.Switches can determinewhether data should remainon a LAN or not, and theycan transfer the data to theconnection that needs thatdata. 10
  11. 11. RouterRouters have all capabilities of the previous devices. Routerscan regenerate signals, concentrate multipleconnections, convert data transmission formats, and managedata transfers.They can also connect to a WAN, which allowsthem to connect LANs that are separated by great distances. 11
  12. 12. ―The Cloud‖The cloud is used in diagrams to represent where theconnection to the internet is.It also represents all of the devices on the internet. 12
  13. 13. Network TopologiesNetwork topology defines the structure of the network.One part of the topology definition is the physicaltopology, which is the actual layout of the wire or media.The other part is the logical topology,which defines how themedia is accessed by the hosts for sending data. 13
  14. 14. Physical Topologies 14
  15. 15. Bus TopologyA bus topology uses a single backbone cable that isterminated at both ends.All the hosts connect directly to this backbone. 15
  16. 16. Ring TopologyA ring topology connects one host to the next and the last hostto the first.This creates a physical ring of cable. 16
  17. 17. Star TopologyA star topology connects all cables to a central point ofconcentration. 17
  18. 18. Extended Star TopologyAn extended star topology links individual stars together byconnecting the hubs and/or switches.This topology can extendthe scope and coverage of the network. 18
  19. 19. Hierarchical TopologyA hierarchical topology is similar to an extended star. 19
  20. 20. Mesh TopologyA mesh topology is implemented to provide as muchprotection as possible from interruption of service.Each host has its own connections to all other hosts.Although the Internet has multiple paths to any onelocation, it does not adopt the full mesh topology. 20
  21. 21. LANs, MANs, & WANsOne early solution was the creation of local-area network(LAN) standards which provided an open set of guidelines forcreating network hardware and software, making equipmentfrom different companies compatible.What was needed was a way for information to moveefficiently and quickly, not only within a company, but alsofrom one business to another.The solution was the creation of metropolitan-area networks(MANs) and wide-area networks (WANs). 21
  22. 22. Examples of Data Networks 22
  23. 23. LANs 23
  24. 24. Wireless LAN Organizations and StandardsIn cabled networks, IEEE is the prime issuer of standards forwireless networks. The standards have been created within theframework of the regulations created by the FederalCommunications Commission (FCC).A key technology contained within the 802.11 standard is DirectSequence Spread Spectrum (DSSS). 24
  25. 25. Cellular Topology for Wireless 25
  26. 26. WANs 26
  27. 27. SANsA SAN is a dedicated, high-performance network used tomove data between serversand storage resources.Because it is aseparate, dedicatednetwork, it avoids any trafficconflict between clients andservers. 27
  28. 28. Virtual Private NetworkA VPN is a private network that is constructed within a public networkinfrastructure such as the global Internet. Using VPN, a telecommutercan access the network of the company headquarters through theInternet by building a secure tunnel between the telecommuter’s PCand a VPN router in the headquarters. 28
  29. 29. Bandwidth 29
  30. 30. Measuring Bandwidth 30
  31. 31. 31
  32. 32. Why do we need the OSI Model?To address the problem of networks increasing in sizeand in number, the International Organization forStandardization (ISO) researched many networkschemes and recognized that there was a need tocreate a network model that would help networkbuilders implement networks that could communicateand work together and therefore, released the OSIreference model in 1984. 32
  33. 33. Don’t Get Confused.ISO - International Organization for StandardizationOSI - Open System InterconnectionIOS - Internetwork Operating SystemThe ISO created the OSI to make the IOS moreefficient. The ―ISO‖ acronym is correct as shown.To avoid confusion, some people say ―InternationalStandard Organization.‖ 33
  34. 34. The OSI Reference Model7 Application The OSI Model will be used throughout your6 Presentation entire networking5 Session career!4 Transport3 Network Memorize it!2 Data Link1 Physical 34
  35. 35. Layer 7 - The Application Layer7 Application This layer deal with networking applications.6 Presentation5 Session Examples:4 Transport  Email  Web browsers3 Network2 Data Link PDU - User Data1 Physical 35
  36. 36. Layer 6 - The Presentation Layer7 Application This layer is responsible for presenting the data in6 Presentation the required format which5 Session may include:4 Transport  Encryption  Compression3 Network2 Data Link PDU - Formatted Data1 Physical 36
  37. 37. Layer 5 - The Session Layer7 Application This layer establishes, manages, and terminates6 Presentation sessions between two5 Session communicating hosts.4 Transport Example:3 Network  Client Software2 Data Link ( Used for logging in)1 Physical PDU - Formatted Data 37
  38. 38. Layer 4 - The Transport Layer7 Application This layer breaks up the data from the sending host6 Presentation and then reassembles it in5 Session the receiver.4 Transport It also is used to insure3 Network reliable data transport2 Data Link across the network.1 Physical PDU - Segments 38
  39. 39. Layer 3 - The Network Layer7 Application Sometimes referred to as the ―Cisco Layer‖.6 Presentation5 Session Makes ―Best Path4 Transport Determination‖ decisions based on logical addresses3 Network (usually IP addresses).2 Data Link PDU - Packets1 Physical 39
  40. 40. Layer 2 - The Data Link Layer7 Application This layer provides reliable transit of data across a6 Presentation physical link.5 Session4 Transport Makes decisions based on physical addresses (usually3 Network MAC addresses).2 Data Link PDU - Frames1 Physical 40
  41. 41. Layer 1 - The Physical Layer This is the physical media7 Application through which the data,6 Presentation represented as electronic signals, is sent from the5 Session source host to the4 Transport destination host.3 Network Examples:2 Data Link  CAT5 (what we have)1 Physical  Coaxial (like cable TV)  Fiber optic PDU - Bits 41
  42. 42. OSI Model AnalogyApplication Layer - Source HostAfter riding your new bicycle a few times inNewYork, you decide that you want to give it to afriend who lives in Munich,Germany. 42
  43. 43. OSI Model AnalogyPresentation Layer - Source HostMake sure you have the proper directions todisassemble and reassemble the bicycle. 43
  44. 44. OSI Model Analogy Session Layer - Source HostCall your friend and make sure you have hiscorrect address. 44
  45. 45. OSI Model Analogy Transport Layer - Source HostDisassemble the bicycle and put different piecesin different boxes. The boxes are labeled ―1 of 3‖, ―2 of 3‖, and ―3 of 3‖. 45
  46. 46. OSI Model Analogy Network Layer - Source HostPut your friends complete mailing address (andyours) on each box.Since the packages are toobig for your mailbox (and since you don’t haveenough stamps) you determine that you need togo to the post office. 46
  47. 47. OSI Model Analogy Data Link Layer – Source HostNewYork post office takes possession of theboxes. 47
  48. 48. OSI Model Analogy Physical Layer - MediaThe boxes are flown from USA to Germany. 48
  49. 49. OSI Model Analogy Data Link Layer - DestinationMunich post office receives your boxes. 49
  50. 50. OSI Model Analogy Network Layer - DestinationUpon examining the destination address,Munich post office determines that yourboxes should be delivered to your writtenhome address. 50
  51. 51. OSI Model Analogy Transport Layer - DestinationYour friend calls you and tells you he got all 3boxes and he is having another friend namedBOB reassemble the bicycle. 51
  52. 52. OSI Model Analogy Session Layer - DestinationYour friend hangs up because he is done talkingto you. 52
  53. 53. OSI Model AnalogyPresentation Layer - DestinationBOB is finished and ―presents‖ the bicycle toyour friend. Another way to say it is that yourfriend is finally getting him ―present‖. 53
  54. 54. OSI Model AnalogyApplication Layer - DestinationYour friend enjoys riding his new bicycle inMunich. 54
  55. 55. Host Layers7 Application These layers only exist in the6 Presentation source and5 Session destination host4 Transport computers.3 Network2 Data Link1 Physical 55
  56. 56. Media Layers7 Application6 Presentation5 Session4 Transport These layers manage3 Network the information out in2 Data Link the LAN or WAN1 Physical between the source and destination hosts. 56
  57. 57. 57
  58. 58. 58
  59. 59. Data Flow Through a Network 59
  60. 60. 60
  61. 61. LAN Physical LayerVarious symbols are used to represent media types.The function of media is to carry a flow of informationthrough a LAN.Networking media are consideredLayer 1, or physical layer, components of LANs.Each media has advantages and disadvantages.Some of the advantage or disadvantage comparisonsconcern:• Cable length• Cost• Ease of installation• Susceptibility to interferenceCoaxial cable, optical fiber, and even free space cancarry network signals. However, the principal mediumthat will be studied is Category 5 unshielded twisted-pair cable (Cat 5 UTP) 61
  62. 62. Unshielded Twisted Pair (UTP) Cable 62
  63. 63. UTP ImplementationEIA/TIA specifies an RJ-45 connector for UTP cable.The RJ-45 transparent end connector shows eight colored wires.Four of the wires carry the voltage and are considered ―tip‖ (T1 through T4).The other four wires are grounded and are called ―ring‖ (R1 through R4).The wires in the first pair in a cable or a connector are designated as T1 & R1 63
  64. 64. Connection MediaThe registered jack (RJ-45) connector and jack are the mostcommon.In some cases the type of connector on a network interfacecard (NIC) does not match the media that it needs to connectto.The attachment unit interface (AUI) connector allows differentmedia to connect when used with the appropriate transceiver.A transceiver is an adapter that converts one type ofconnection to another. 64
  65. 65. Ethernet StandardsThe Ethernet standard specifies that each of the pins on anRJ-45 connector have a particular purpose. A NIC transmitssignals on pins 1 & 2, and it receives signals on pins 3 & 6. 65
  66. 66. Remember…A straight-thru cable has T568B on both ends. A crossover (orcross-connect) cable has T568B on one end and T568A on theother. A console cable had T568B on one end and reverse T568Bon the other, which is why it is also called a rollover cable. 66
  67. 67. Straight-Thru or CrossoverUse straight-through cables for the following cabling:• Switch to router• Switch to PC or server• Hub to PC or serverUse crossover cables for the following cabling:• Switch to switch• Switch to hub• Hub to hub• Router to router• PC to PC• Router to PC 67
  68. 68. Sources of Noise on Copper MediaNoise is any electrical energy on thetransmission cable that makes it difficult for areceiver to interpret the data sent from thetransmitter. TIA/EIA-568-B certification of a cablenow requires testing for a variety of types ofnoise.Twisted-pair cable is designed to takeadvantage of the effects of crosstalk in order tominimize noise. In twisted-pair cable, a pair ofwires is used to transmit one signal.The wire pairis twisted so that each wire experiences similarcrosstalk. Because a noise signal on one wirewill appear identically on the other wire, thisnoise be easily detected and filtered atreceiver.Twisting one pair of wires in a cable alsohelps to reduce crosstalk of data or noise signalsfrom adjacent wires. 68
  69. 69. Shielded Twisted Pair (STP) Cable 69
  70. 70. Coaxial Cable 70
  71. 71. Fiber Optic Cable 71
  72. 72. Fiber Optic ConnectorsConnectors are attached to the fiber ends so that the fibers canbe connected to the ports on the transmitter and receiver.The type of connector most commonly used with multimode fiberis the Subscriber Connector (SC connector).On single-modefiber, the Straight Tip (ST) connector is frequently used 72
  73. 73. Fiber Optic Patch PanelsFiber patch panels similar to the patch panels used with coppercable. 73
  74. 74. Cable Specifications10BASE-TThe T stands for twisted pair.10BASE5The 5 represents the fact that a signal can travel for approximately500 meters 10BASE5 is often referred to as Thicknet.10BASE2The 2 represents the fact that a signal can travel for approximately200 meters 10BASE2 is often referred to as Thinnet.All 3 of these specifications refer to the speed of transmission at 10Mbps and a type of transmission that is baseband, or digitallyinterpreted. Thinnet and Thicknet are actually a type ofnetworks, while 10BASE2 & 10BASE5 are the types of cabling used inthese networks. 74
  75. 75. Ethernet Media Connector Requirements 75
  76. 76. LAN Physical Layer Implementation 76
  77. 77. Ethernet in the Campus 77
  78. 78. WAN Physical Layer 78
  79. 79. WAN Serial Connection Options 79
  80. 80. Serial Implementation of DTE & DCE When connecting directly to a service provider, or to a device such as a CSU/DSU that will perform signal clocking, the router is a DTE and needs a DTE serial cable. This is typically the case for routers. 80
  81. 81. Back-to-Back Serial ConnectionWhenperforming aback-to-backrouter scenarioin a testenvironment, one of the routerswill be a DTEand the otherwill be a DCE. 81
  82. 82. RepeaterA repeater is a network device used to regenerate a signal.Repeaters regenerate analog or digital signals distorted bytransmission loss due to attenuation.Repeater is a PhysicalLayer device 82
  83. 83. The 4 Repeater RuleThe Four Repeater Rule for 10-Mbps Ethernet should beused as a standard when extending LAN segments.This rule states that no more than four repeaterscan be used between hosts on a LAN.This rule is used to limit latency added to frame travel byeach repeater. 83
  84. 84. HubHubs concentrateconnections.In otherwords, they take a group ofhosts and allow the networkto see them as a single unit.Hub is a physical layerdevice. 84
  85. 85. Network Interface CardThe function of a NIC is to connect a host device to the network medium.A NIC is a printed circuit board that fits into the expansion slot on the motherboard orperipheral device of a computer. The NIC is also referred to as a network adapter.NICs are considered Data Link Layer devices because each NIC carries aunique code called a MAC address. 85
  86. 86. MAC AddressMAC address is 48 bits in length and expressed as twelve hexadecimaldigits.MAC addresses are sometimes referred to as burned-in addresses(BIA) because they are burned into read-only memory (ROM) and arecopied into random-access memory (RAM) when the NIC initializes. 86
  87. 87. BridgeBridges are Data Link layer devices.Connected hostaddresses are learned and stored on a MAC addresstable.Each bridge port has a unique MAC address 87
  88. 88. Bridges 88
  89. 89. Bridging Graphic 89
  90. 90. SwitchSwitches are Data Linklayer devices.Each Switch port has aunique MAC address.Connected host MACaddresses are learned andstored on a MAC addresstable. 90
  91. 91. Switching Modescut-throughA switch starts to transfer the frame as soon as the destination MACaddress is received. No error checking is available.Must use synchronous the other extreme, the switch can receive the entire frame beforesending it out the destination port. This gives the switch software anopportunity to verify the Frame Check Sum (FCS) to ensure that the framewas reliably received before sending it to the destination.Must be used with asynchronous switching.fragment-freeA compromise between the cut-through and store-and-forward modes.Fragment-free reads the first 64 bytes, which includes the frameheader, and switching begins before the entire data field and checksumare read. 91
  92. 92. Full DuplexAnother capability emerges when only two nodes are connected. In a network thatuses twisted-pair cabling, one pair is used to carry the transmitted signal from onenode to the other node. A separate pair is used for the return or received signal. It ispossible for signals to pass through both pairs simultaneously. The capability ofcommunication in both directions at once is known as full duplex. 92
  93. 93. Switches – MAC Tables 93
  94. 94. Switches – Parallel Communication 94
  95. 95. MicrosegmentationA switch is simply a bridge with many ports. When only one node is connected to aswitch port, the collision domain on the shared media contains only two nodes.The two nodes in this small segment, or collision domain, consist of the switch portand the host connected to it. These small physical segments are called microsegments. 95
  96. 96. Peer-to-Peer NetworkIn a peer-to-peer network, networked computers act as equal partners, or peers.As peers, each computer can take on the client function or the server function.At one time, computer A may make a request for a file from computer B, whichresponds by serving the file to computer A. Computer A functions as client, while Bfunctions as the server. At a later time, computers A and B can reverse roles.In a peer-to-peer network, individual users control their own resources. Peer-to-peer networks are relatively easy to install and operate. As networks grow, peer-to-peer relationships become increasingly difficult to coordinate. 96
  97. 97. Client/Server NetworkIn a client/server arrangement, network services are located on a dedicatedcomputer called a server.The server responds to the requests of clients.The server is a central computer that is continuously available to respond torequests from clients for file, print, application, and other services.Most network operating systems adopt the form of a client/server relationship. 97
  98. 98. 98
  99. 99. Why Another Model?Although the OSI reference model is universallyrecognized, the historical and technical open standardof the Internet is Transmission Control Protocol /Internet Protocol (TCP/IP).The TCP/IP reference model and the TCP/IP protocolstack make data communication possible between anytwo computers, anywhere in the world, at nearly thespeed of light.The U.S. Department of Defense (DoD) created theTCP/IP reference model because it wanted a networkthat could survive any conditions, even a nuclear war. 99
  100. 100. Don’t Confuse the Models7 Application6 Presentation Application5 Session4 Transport Transport3 Network Internet2 Data Link Network1 Physical Access 100
  101. 101. 2 Models Side-By-Side7 Application6 Presentation Application5 Session4 Transport Transport3 Network Internet2 Data Link Network1 Physical Access 101
  102. 102. The Application LayerThe applicationlayer of theTCP/IP modelhandles high-levelprotocols, issues ofrepresentation,encoding, anddialog control. 102
  103. 103. The Transport LayerThe transport layer provides transport services fromthe source host to the destination host. It constitutesa logical connection between these endpoints of thenetwork. Transport protocols segment andreassemble upper-layer applications into the samedata stream between endpoints.The transport layer data stream provides end-to-endtransport services. 103
  104. 104. The Internet Layer The purpose of the Internet layer is to select the best path through the network for packets to travel. The main protocol that functions at this layer is the Internet Protocol (IP). Best path determination and packet switching occur at this layer. 104
  105. 105. The Network Access Layer The network access layer is also called the host-to- network layer. It the layer that is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media. It includes LAN and WAN details, and all the details contained in the OSI physical and data-link layers. NOTE: ARP & RARP work at both the Internet and Network Access Layers. 105
  106. 106. Comparing TCP/IP & OSI ModelsNOTE: TCP/IP transport layer using UDP does not always guaranteereliable delivery of packets as the transport layer in the OSI model does. 106
  107. 107. Introduction to the Transport LayerThe primary duties of the transport layer, Layer 4 of the OSImodel, are to transport and regulate the flow of information fromthe source to the destination, reliably and accurately.End-to-end control and reliability are provided by slidingwindows, sequencing numbers, and acknowledgments. 107
  108. 108. More on The Transport LayerThe transport layer provides transport services from thesource host to the destination host.It establishes a logical connection between the endpoints ofthe network.• Transport services include the following basic services:• Segmentation of upper-layer application data• Establishment of end-to-end operations• Transport of segments from one end host to another end host• Flow control provided by sliding windows• Reliability provided by sequence numbers and acknowledgments 108
  109. 109. Flow ControlAs the transport layer sends data segments, it tries to ensure that data is not lost.A receiving host that is unable to process data as quickly as it arrives could be acause of data loss.Flow control avoids the problem of a transmitting host overflowing the buffers inthe receiving host. 109
  110. 110. 3-Way HandshakeTCP requires connection establishment before data transfer begins.For a connection to be established or initialized, the two hosts mustsynchronize their Initial Sequence Numbers (ISNs). 110
  111. 111. Basic WindowingData packets must bedelivered to therecipient in the sameorder in which theywere transmitted tohave areliable, connection-oriented data transfer.The protocol fails ifany data packets arelost, damaged, duplicated, or received in adifferent order.An easy solution is tohave a recipientacknowledge thereceipt of each packetbefore the nextpacket is sent. 111
  112. 112. Sliding Window 112
  113. 113. Sliding Windowwith Different Window Sizes 113
  114. 114. TCP Sequence & Acknowledgement 114
  115. 115. TCPTransmission Control Protocol (TCP) is a connection-oriented Layer 4protocol that provides reliable full-duplex data transmission.TCP is part of the TCP/IP protocol stack. In a connection-orientedenvironment, a connection is established between both ends before thetransfer of information can begin.TCP is responsible for breaking messages into segments, reassemblingthem at the destination station, resending anything that is not received,and reassembling messages from the segments.TCP supplies a virtualcircuit between end-user applications.The protocols that use TCP include:• FTP (File Transfer Protocol)• HTTP (Hypertext Transfer Protocol)• SMTP (Simple Mail Transfer Protocol)• Telnet 115
  116. 116. TCP Segment Format 116
  117. 117. UDPUser Datagram Protocol (UDP) is the connectionless transport protocolin the TCP/IP protocol stack.UDP is a simple protocol that exchanges datagrams, withoutacknowledgments or guaranteed delivery. Error processing andretransmission must be handled by higher layer protocols.UDP uses no windowing or acknowledgments so reliability, if needed, isprovided by application layer protocols. UDP is designed for applicationsthat do not need to put sequences of segments together.The protocols that use UDP include:• TFTP (Trivial File Transfer Protocol)• SNMP (Simple Network Management Protocol)• DHCP (Dynamic Host Control Protocol)• DNS (Domain Name System) 117
  118. 118. UDP Segment Format 118
  119. 119. Well Known Port NumbersThe following port numbers should be memorized:NOTE:The curriculum forgot to mention one of the most important port numbers.Port 80 is used for HTTP or WWW protocols. (Essentially access to the internet.) 119
  120. 120. URL 120
  121. 121. SNMP – Managed Network 121
  122. 122. 122
  123. 123. Base 2 Number System101102 = (1 x 24 = 16) + (0 x 23 = 0) + (1 x 22 = 4) + (1 x 21 = 2) + (0 x 20 = 0) = 22 123
  124. 124. Converting Decimal to BinaryConvert 20110 to binary: 201 / 2 = 100 remainder 1 100 / 2 = 50 remainder 0 50 / 2 = 25 remainder 0 25 / 2 = 12 remainder 1 12 / 2 = 6 remainder 0 6 / 2 = 3 remainder 0 3 / 2 = 1 remainder 1 1 / 2 = 0 remainder 1When the quotient is 0, take all the remainders inreverse order for your answer: 20110 = 110010012 124
  125. 125. 125
  126. 126. Network and Host AddressingUsing the IP address of thedestination network, a router candeliver a packet to the correctnetwork.When the packet arrives at arouter connected to thedestination network, the routeruses the IP address to locate theparticular computer connected tothat network.Accordingly, every IP address hastwo parts. 126
  127. 127. Network Layer Communication PathA router forwards packets from the originating network to thedestination network using the IP protocol. The packets mustinclude an identifier for both the source and destination networks. 127
  128. 128. Internet AddressesIP Addressing is a hierarchical structure.An IP address combines twoidentifiers into one number. This number must be a uniquenumber, because duplicate addresses would make routingimpossible.The first part identifies the systems network address.Thesecond part, called the host part, identifies which particular machineit is on the network. 128
  129. 129. IP Address ClassesIP addresses are divided into classes to define thelarge, medium, and small networks.Class A addresses are assigned to larger networks.Class B addresses are used for medium-sized networks, &Class C for small networks. 129
  130. 130. Identifying Address Classes 130
  131. 131. Address Class PrefixesTo accommodate different size networks and aid in classifying these networks, IPaddresses are divided into groups called classes.This is classful addressing. 131
  132. 132. Network and Host DivisionEach complete 32-bit IP address is broken down into a network partand a host part. A bit or bit sequence at the start of each addressdetermines the class of the address. There are 5 IP address classes. 132
  133. 133. Class A AddressesThe Class A address was designed to support extremely largenetworks, with more than 16 million host addresses available.Class A IP addresses use only the first octet to indicate thenetwork address. The remaining three octets provide for hostaddresses. 133
  134. 134. Class B AddressesThe Class B address was designed to support the needs ofmoderate to large-sized networks.A Class B IP address usesthe first two of the four octets to indicate the network address.The other two octets specify host addresses. 134
  135. 135. Class C AddressesThe Class C address space is the most commonly used of theoriginal address classes.This address space was intended tosupport small networks with a maximum of 254 hosts. 135
  136. 136. Class D AddressesThe Class D address class was created to enable multicasting in anIP address. A multicast address is a unique network address thatdirects packets with that destination address to predefined groups ofIP addresses. Therefore, a single station can simultaneously transmita single stream of data to multiple recipients. 136
  137. 137. Class E AddressesA Class E address has been defined. However, the InternetEngineering Task Force (IETF) reserves these addresses for itsown research. Therefore, no Class E addresses have beenreleased for use in the Internet. 137
  138. 138. IP Address RangesThe graphic below shows the IP address range of the first octetboth in decimal and binary for each IP address class. 138
  139. 139. IPv4As early as 1992, the Internet EngineeringTask Force (IETF) identified two specificconcerns: Exhaustion of theremaining, unassigned IPv4 networkaddresses and the increase in the size ofInternet routing tables.Over the past two decades, numerousextensions to IPv4 have been developed.Two of the more important of these aresubnet masks and classless interdomainrouting (CIDR). 139
  140. 140. Finding the Network Address with ANDingBy ANDing the Host address of with network mask) we obtain the network address of 140
  141. 141. Network Address 141
  142. 142. Broadcast Address 142
  143. 143. Network/Broadcast Addresses at the Binary LevelAn IP address that has binary 0s in all host bit positions isreserved for the network address, which identifies the network.An IP address that has binary 1s in all host bit positions isreserved for the broadcast address, which is used to send datato all hosts on the network. Here are some examples:Class Network Address Broadcast AddressA 143
  144. 144. Public IP AddressesUnique addresses are required for each device on a network.Originally, an organization known as the Internet Network InformationCenter (InterNIC) handled this procedure.InterNIC no longer exists and has been succeeded by the Internet AssignedNumbers Authority (IANA).No two machines that connect to a public network can have the same IPaddress because public IP addresses are global and standardized.All machines connected to the Internet agree to conform to the system.Public IP addresses must be obtained from an Internet service provider(ISP) or a registry at some expense. 144
  145. 145. Private IP AddressesPrivate IP addresses are another solution to the problem of theimpending exhaustion of public IP addresses.As mentioned, publicnetworks require hosts to have unique IP addresses.However, private networks that are not connected to the Internet mayuse any host addresses, as long as each host within the privatenetwork is unique. 145
  146. 146. Mixing Public and Private IP AddressesPrivate IP addresses can be intermixed, as shown in the graphic, withpublic IP addresses.This will conserve the number of addresses used forinternal connections. Connecting a network using private addresses tothe Internet requires translation of the private addresses to publicaddresses. This translation process is referred to as Network AddressTranslation (NAT). 146
  147. 147. Introduction to SubnettingSubnetting a network means to use the subnet mask to divide thenetwork and break a large network up into smaller, more efficient andmanageable segments, or subnets.With subnetting, the network is not limited to the default Class A, B, orC network masks and there is more flexibility in the network design.Subnet addresses include the network portion, plus a subnet field anda host field.The ability to decide how to divide the original host portioninto the new subnet and host fields provides addressing flexibility forthe network administrator. 147
  148. 148. The 32-BitBinary IP Address 148
  149. 149. Numbers That Show Up InSubnet Masks (Memorize Them!) 149
  150. 150. Addressing with Subnetworks 150
  151. 151. Obtaining an Internet Address 151
  152. 152. Static Assignment of an IP AddressStatic assignmentworks best on smallnetworks.The administratormanually assigns andtracks IP addressesfor eachcomputer, printer, orserver on the intranet.Networkprinters, applicationservers, and routersshould be assignedstatic IP addresses. 152
  153. 153. ARP(Address Resolution Protocol)Host A ARP Request - Broadcast to all hosts SIEMENS NIXDORF „What is the hardware address for IP address― ARP Reply SIEMENS NIXDORF SIEMENS NIXDORF Host B IP Address: HW Address: 080020021545 153 Fig. 32 How does ARP work? (TI1332EU02TI_0004 The Network Layer, 47)
  154. 154. 154Fig. 33 The ARP command (TI1332EU02TI_0004 The Network Layer, 47)
  155. 155. 1 Network = 1 Broadcast Domain A B host B would reply Broadcast: ARP request 2 Networks = 2 Broadcast Domains A B no one would reply RouterBroadcast: ARP request 155 Fig. 34 Proxy-ARP concept (TI1332EU02TI_0004 The Network Layer, 49)
  156. 156. A B A B Router R I take care, to forward IP packets to B Broadcast Message to all:If your IP address matches ―B‖ Yes, I know the destination then please tell me your network, let me give you my Ethernet address Ethernet address 156
  157. 157. RARPReverse Address Resolution Protocol (RARP) associates a known MAC addresseswith an IP addresses.A network device, such as a diskless workstation, might know its MAC address but notits IP address. RARP allows the device to make a request to learn its IP address.Devices using RARP require that a RARP server be present on the network to answerRARP requests. 157
  158. 158. BootPThe bootstrap protocol (BOOTP) operates in a client-server environment and onlyrequires a single packet exchange to obtain IP information.However, unlike RARP, BOOTP packets can include the IP address, as well asthe address of a router, the address of a server, and vendor-specific information.One problem with BOOTP, however, is that it was not designed to providedynamic address assignment. With BOOTP, a network administrator creates aconfiguration file that specifies the parameters for each device.The administratormust add hosts and maintain the BOOTP database.Even though the addresses are dynamically assigned, there is still a one to onerelationship between the number of IP addresses and the number of hosts.This means that for every host on the network there must be a BOOTP profilewith an IP address assignment in it. No two profiles can have the same IPaddress. 158
  159. 159. DHCPDynamic host configuration protocol (DHCP) is the successor to BOOTP.Unlike BOOTP, DHCP allows a host to obtain an IP address dynamically without thenetwork administrator having to set up an individual profile for each device.All that is required when using DHCP is a defined range of IP addresses on a DHCPserver.As hosts come online, they contact the DHCP server and request an address.The DHCP server chooses an address and leases it to that host.With DHCP, the entire network configuration of a computer can be obtained in onemessage.This includes all of the data supplied by the BOOTP message, plus a leased IPaddress and a subnet mask.The major advantage that DHCP has over BOOTP is that it allows users to be mobile. 159
  160. 160. 160
  161. 161. Introduction to RoutersA router is a special type of computer. It has the same basic components as astandard desktop PC. However, routers are designed to perform some very specificfunctions. Just as computers need operating systems to run softwareapplications, routers need the Internetwork Operating System software (IOS) to runconfiguration files. These configuration files contain the instructions and parametersthat control the flow of traffic in and out of the routers. The many parts of a router areshown below: 161
  162. 162. RAMRandom Access Memory, also called dynamic RAM (DRAM)RAM has the following characteristics and functions:• Stores routing tables• Holds ARP cache• Holds fast-switching cache• Performs packet buffering (shared RAM)• Maintains packet-hold queues• Provides temporary memory for the configuration file of the router while the router is powered on• Loses content when router is powered down or restarted 162
  163. 163. NVRAMNon-Volatile RAMNVRAM has the following characteristics and functions:• Provides storage for the startup configuration file• Retains content when router is powered down or restarted 163
  164. 164. FlashFlash memory has the following characteristics andfunctions:• Holds the operating system image (IOS)• Allows software to be updated without removing and replacing chips on the processor• Retains content when router is powered down or restarted• Can store multiple versions of IOS softwareIs a type of electronically erasable, programmableROM (EEPROM) 164
  165. 165. ROMRead-Only MemoryROM has the following characteristics and functions:• Maintains instructions for power-on self test (POST) diagnostics• Stores bootstrap program and basic operating system software• Requires replacing pluggable chips on the motherboard for software upgrades 165
  166. 166. InterfacesInterfaces have the following characteristics and functions:• Connect router to network for frame entry and exit• Can be on the motherboard or on a separate moduleTypes of interfaces:• Ethernet• Fast Ethernet• Serial• Token ring• ISDN BRI• Loopback• Console• Aux 166
  167. 167. Internal Components of a 2600 Router 167
  168. 168. External Components of a 2600 Router 168
  169. 169. External Connections 169
  170. 170. Fixed InterfacesWhen cabling routers for serial connectivity, the routers will either havefixed or modular ports. The type of port being used will affect the syntaxused later to configure each interface. Interfaces on routers with fixedserial ports are labeled for port type and port number. 170
  171. 171. Modular Serial Port InterfacesInterfaces on routers with modular serial ports are labeled for port type, slot, and portnumber.The slot is the location of the module.To configure a port on a modular card, it isnecessary to specify the interface using the syntax ―port type slot number/port number.‖ Usethe label ―serial 0/1,‖ when the interface is serial, the slot number where the module isinstalled is slot 0, and the port that is being referenced is port 1. 171
  172. 172. Routers & DSL ConnectionsThe Cisco 827 ADSL router has one asymmetric digitalsubscriber line (ADSL) interface. To connect a router for DSLservice, use a phone cable with RJ-11 connectors. DSL worksover standard telephone lines using pins 3 and 4 on astandard RJ-11 connector. 172
  173. 173. Computer/Terminal Console Connection 173
  174. 174. Modem Connection to Console/Aux Port 174
  175. 175. HyperTerminal Session Properties 175
  176. 176. Establishing a HyperTerminal SessionTake the following stepsto connect a terminal tothe console port on therouter:First, connect theterminal using the RJ-45to RJ-45 rollover cableand an RJ-45 to DB-9 orRJ-45 to DB-25 adapter.Then, configure theterminal or PC terminalemulation software for9600 baud, 8 data bits,no parity, 1 stop bit, andno flow control. 176
  177. 177. Cisco IOSCisco technology is built around the CiscoInternetwork Operating System (IOS), which is thesoftware that controls the routing and switchingfunctions of internetworking devices.A solid understanding of the IOS is essential for anetwork administrator. 177
  178. 178. The Purpose of Cisco IOSAs with a computer, a router or switch cannot function withoutan operating system. Cisco calls its operating system theCisco Internetwork Operating System or Cisco IOS.It is the embedded software architecture in all of the Ciscorouters and is also the operating system of the Catalystswitches.Without an operating system, the hardware does not have anycapabilities.The Cisco IOS provides the following network services:• Basic routing and switching functions• Reliable and secure access to networked resources• Network scalability 178
  179. 179. Router Command Line Interface 179
  180. 180. Setup ModeSetup is not intended as the mode for entering complex protocol features in therouter. The purpose of the setup mode is to permit the administrator to install aminimal configuration for a router, unable to locate a configuration from anothersource.In the setup mode, default answers appear in square brackets [ ] following thequestion. Press the Enter key to use these defaults.During the setup process, Ctrl-C can be pressed at any time to terminate theprocess. When setup is terminated using Ctrl-C, all interfaces will beadministratively shutdown.When the configuration process is completed in setup mode, the following optionswill be displayed:[0] Go to the IOS command prompt without saving this config.[1] Return back to the setup without saving this config.[2] Save this configuration to nvram and exit.Enter your selection [2]: 180
  181. 181. Operation of Cisco IOS SoftwareThe Cisco IOS devices have three distinct operating environments ormodes:• ROM monitor• Boot ROM• Cisco IOSThe startup process of the router normally loads into RAM and executesone of these operating environments. The configuration register setting canbe used by the system administrator to control the default start up mode forthe router.To see the IOS image and version that is running, use the show versioncommand, which also indicates the configuration register setting. 181
  182. 182. IOS File System Overview 182
  183. 183. Initial Startup of Cisco RoutersA router initializes by loading the bootstrap, the operating system, and aconfiguration file.If the router cannot find a configuration file, it enters setup mode.Upon completion of the setup mode a backup copy of the configuration filemay be saved to nonvolatile RAM (NVRAM).The goal of the startup routines for Cisco IOS software is to start the routeroperations. To do this, the startup routines must accomplish the following:• Make sure that the router hardware is tested and functional.• Find and load the Cisco IOS software.• Find and apply the startup configuration file or enter the setup mode.When a Cisco router powers up, it performs a power-on self test (POST).During this self test, the router executes diagnostics from ROM on allhardware modules. 183
  184. 184. After the Post…After the POST, the following events occur as the router initializes:Step 1The generic bootstrap loader in ROM executes. A bootstrap is a simple set ofinstructions that tests hardware and initializes the IOS for operation.Step 2The IOS can be found in several places. The boot field of the configuration registerdetermines the location to be used in loading the IOS. If the boot field indicates aflash or network load, boot system commands in the configuration file indicate theexact name and location of the image.Step 3The operating system image is loaded.Step 4The configuration file saved in NVRAM is loaded into main memory and executedone line at a time. The configuration commands start routing processes, supplyaddresses for interfaces, and define other operating characteristics of the router.Step 5If no valid configuration file exists in NVRAM, the operating system searches for an 184available TFTP server. If no TFTP server is found, the setup dialog is initiated.
  185. 185. Step in Router Initialization 185
  186. 186. Router LED IndicatorsCisco routers use LED indicators to provide status information.Depending upon the Cisco router model, the LED indicators willvary. An interface LED indicates the activity of the correspondinginterface. If an LED is off when the interface is active and theinterface is correctly connected, a problem may be indicated. If aninterface is extremely busy, its LED will always be on. The green OKLED to the right of the AUX port will be on after the system initializescorrectly. 186
  187. 187. EnhancedCisco IOS Commands 187
  188. 188. The show version CommandThe show version command displays information about the Cisco IOSsoftware version that is currently running on the router. This includes theconfiguration register and the boot field settings.The following information is available from the show version command: IOS version and descriptive information• Bootstrap ROM version• Boot ROM version• Router up time• Last restart method• System image file and location• Router platform• Configuration register settingUse the show version command to identify router IOS image and bootsource. To find out the amount of flash memory, issue the show flashcommand. 188
  189. 189. 189
  190. 190. 190
  191. 191. Router User Interface ModesThe Cisco command-line interface (CLI) uses a hierarchical structure. Thisstructure requires entry into different modes to accomplish particular tasks.Each configuration mode is indicated with a distinctive prompt and allowsonly commands that are appropriate for that mode.As a security feature the Cisco IOS software separates sessions into twoaccess levels, user EXEC mode and privileged EXEC mode. The privilegedEXEC mode is also known as enable mode. 191
  192. 192. Overview of Router Modes 192
  193. 193. Router Modes 193
  194. 194. User Mode Commands 194
  195. 195. Privileged Mode Commands NOTE: There are many more commands available in privileged mode. 195
  196. 196. Specific Configuration Modes 196
  197. 197. CLI Command ModesAll command-line interface (CLI) configuration changes to a Cisco routerare made from the global configuration mode. Other more specific modesare entered depending upon the configuration change that is required.Global configuration mode commands are used in a router to applyconfiguration statements that affect the system as a whole.The following command moves the router into global configuration modeRouter#configure terminal (or config t)Router(config)#When specific configuration modes are entered, the router prompt changesto indicate the current configuration mode.Typing exit from one of these specific configuration modes will return therouter to global configuration mode. Pressing Ctrl-Z returns the router to allthe way back privileged EXEC mode. 197
  198. 198. Configuring a Router’s NameA router should be given a unique name as one of thefirst configuration tasks.This task is accomplished in global configurationmode using the following commands:Router(config)#hostname TokyoTokyo(config)#As soon as the Enter key is pressed, the promptchanges from the default host name (Router) to thenewly configured host name (which is Tokyo in theexample above). 198
  199. 199. Settingthe Clockwith Help 199
  200. 200. Message Of The Day (MOTD)A message-of-the-day (MOTD) banner can be displayed on all connected terminals.Enter global configuration mode by using the command config tEnter the commandbanner motd # The message of the day goes here #.Save changes by issuing the command copy run start 200
  201. 201. Configuring a Console PasswordPasswords restrict access to routers.Passwords should always be configured for virtual terminallines and the console line.Passwords are also used to control access to privileged EXECmode so that only authorized users may make changes to theconfiguration file.The following commands are used to set an optional butrecommended password on the console line:Router(config)#line console 0Router(config-line)#password <password>Router(config-line)#login 201
  202. 202. Configuring a Modem PasswordIf configuring a router via a modem you are most likelyconnected to the aux port.The method for configuring the aux port is very similar toconfiguring the console port.Router(config)#line aux 0Router(config-line)#password <password>Router(config-line)#login 202
  203. 203. Configuring InterfacesAn interface needs an IP Address and a Subnet Mask to be configured.All interfaces are ―shutdown‖ by default.The DCE end of a serial interface needs a clock rate.Router#config tRouter(config)#interface serial 0/1Router(config-if)#ip address rate 56000 (required for serial DCE only)Router(config-if)#no shutdownRouter(config-if)#exitRouter(config)#int f0/0Router(config-if)#ip address shutdownRouter(config-if)#exitRouter(config)#exitRouter#On older routers, Serial 0/1 would be just Serial 1 and f0/0 would be e0.s = serial e = Ethernet f = fast Ethernet 203
  204. 204. Configuring a Telnet PasswordA password must be set on one or more of the virtual terminal(VTY) lines for users to gain remote access to the router usingTelnet.Typically Cisco routers support five VTY lines numbered 0through 4.The following commands are used to set the same passwordon all of the VTY lines:Router(config)#line vty 0 4Router(config-line)#password <password>Router(config-line)#login 204
  205. 205. Examining the show CommandsThere are many show commands that can be used to examine the contents of filesin the router and for troubleshooting. In both privileged EXEC and user EXECmodes, the command show ? provides a list of available show commands. The listis considerably longer in privileged EXEC mode than it is in user EXEC interfaces – Displays all the statistics for all the interfaces on the int s0/1 – Displays statistics for interface Serial 0/1show controllers serial – Displays information-specific to the interface hardwareshow clock – Shows the time set in the routershow hosts – Displays a cached list of host names and addressesshow users – Displays all users who are connected to the routershow history – Displays a history of commands that have been enteredshow flash – Displays info about flash memory and what IOS files are stored thereshow version – Displays info about the router and the IOS that is running in RAMshow ARP – Displays the ARP table of the routershow start – Displays the saved configuration located in NVRAMshow run – Displays the configuration currently running in RAMshow protocol – Displays the global and interface specific status of any configured Layer 3 protocols 205
  206. 206. 206
  207. 207. 207
  208. 208. 208
  209. 209. Ethernet OverviewEthernet is now the dominant LAN technology in the world.Ethernet is not one technology but a family of LANtechnologies.All LANs must deal with the basic issue of how individualstations (nodes) are named, and Ethernet is no exception.Ethernet specifications support different media, bandwidths,and other Layer 1 and 2 variations.However, the basic frame format and addressing scheme isthe same for all varieties of Ethernet. 209
  210. 210. Ethernet and the OSI ModelEthernetoperates in twoareas of theOSI model, thelower half ofthe data linklayer, known asthe MACsublayer andthe physicallayer 210
  211. 211. Ethernet TechnologiesMapped to the OSI Model 211
  212. 212. Layer 2 FramingFraming is the Layer 2 encapsulation process.A frame is the Layer 2 protocol data unit.The frame format diagram shows different groupings of bits(fields) that perform other functions. 212
  213. 213. Ethernet and IEEE FrameFormats are Very Similar 213
  214. 214. 3 Common Layer 2 TechnologiesEthernetUses CSMA/CD logical bus topology(information flow is on a linear bus)physical star or extended star (wired asa star)Token Ringlogical ring topology (information flow iscontrolled in a ring) and a physical startopology (in other words, it is wired as astar)FDDIlogical ring topology (information flow iscontrolled in a ring) and physical dual-ring topology(wired as a dual-ring) 214
  215. 215. Collision DomainsTo move data between one Ethernet station andanother, the data often passes through a repeater.All other stations in the same collision domain seetraffic that passes through a repeater.A collision domain is then a shared resource.Problems originating in one part of the collisiondomain will usually impact the entire collisiondomain. 215
  216. 216. CSMA/CD Graphic 216
  217. 217. BackoffAfter a collision occurs and all stations allow the cable tobecome idle (each waits the full interframe spacing), then thestations that collided must wait an additional and potentiallyprogressively longer period of time before attempting toretransmit the collided frame.The waiting period is intentionally designed to be random sothat two stations do not delay for the same amount of timebefore retransmitting, which would result in more collisions. 217
  218. 218. 218
  219. 219. Hierarchical Addressing Using Variable-Length Subnet Masks© 2003, Cisco Systems, Inc. All rights reserved. 219
  220. 220. Prefix Length and Network MaskRange of Addresses: through Fourth Octet • Have the first 28 bits in common, which is 64 01000000 represented by a /28 prefix length 65 01000001 • 28 bits in common can also be represented in dotted 66 01000010 decimal as 67 01000011 68 01000100Binary ones in the network mask represent network bits in the 69 01000101accompanying IP address; binary zeros represent host bits 70 01000110 11000000.10101000.00000001.0100xxxx IP Address 71 01000111 11111111.11111111.11111111.11110000 Network 72 01001000 Mask 73 01001001In the IP network number that accompanies the network 74 01001010mask, when the host bits of the IP network number are: 75 01001011 • All binary zeros – that address is the bottom of the 76 01001100 address range 77 01001101 • All binary ones – that address is the top of the 78 01001110 address range 220 79 01001111
  221. 221. Implementing VLSM 221
  222. 222. Range Of Addresses for VLSM 222
  223. 223. Breakdown Address Space for Largest Subnet 223
  224. 224. Breakdown Address Spacefor Ethernets at Remote Sites 224
  225. 225. Address Space for Serial Subnets 225
  226. 226. Calculating VLSM: Binary 226
  227. 227. Route Summarization and Classless Interdomain Routing© 2003, Cisco Systems, Inc. All rights reserved. 227
  228. 228. What Is Route Summarization? 228
  229. 229. Summarizing Within an Octet 229
  230. 230. Summarizing Addresses in a VLSM-Designed Network 230
  231. 231. Classless Interdomain Routing–CIDR is a mechanism developed to alleviate exhaustion of addresses and reduce routing table size.–Block addresses can be summarized into single entries without regard to the classful boundary of the network number.–Summarized blocks are installed in routing tables. 231
  232. 232. What Is CIDR?• Addresses are the same as in the route summarization figure, except that Class B network 172 has been replaced by Class C network 192. 232
  233. 233. CIDR Example 233
  234. 234. 234
  235. 235. Anatomy of an IP PacketIP packets consist of the data from upper layers plus an IPheader. The IP header consists of the following: 235
  236. 236. 236
  237. 237. 237
  238. 238. 238
  239. 239. Administrative DistanceThe administrative distance is an optional parameter that gives a measureof the reliability of the route. The range of an AD is 0-255 where smallernumbers are more desireable.The default administrative distance when using next-hop address is 1, whilethe default administrative distance when using the outgoing interface is 0.You can statically assign an AD as follows: Router(config)#ip route 130Sometimes static routes are used for backup purposes. A static route canbe configured on a router that will only be used when the dynamicallylearned route has failed. To use a static route in this manner, simply set theadministrative distance higher than that of the dynamic routing protocolbeing used. 239
  240. 240. Configuring Default RoutesDefault routes are used to route packets with destinations that donot match any of the other routes in the routing table.A default route is actually a special static route that uses this format:ip route [next-hop-address | outgoing interface]This is sometimes referred to as a ―Quad-Zero‖ route.Example using next hop address:Router(config)#ip route using the exit interface: Router(config)#ip route s0/0 240
  241. 241. Verifying Static Route ConfigurationAfter static routes are configured it is important toverify that they are present in the routing table andthat routing is working as expected.The command show running-config is used to viewthe active configuration in RAM to verify that the staticroute was entered correctly.The show ip route command is used to make surethat the static route is present in the routing table. 241
  242. 242. 242
  243. 243. Path Determination Graphic 243
  244. 244. Routing Protocol Router Switch Router Router Router RouterSwitch What is an optimal route ? 244
  245. 245. Routing ProtocolsRouting protocolsincludes the following:processes for sharingroute informationallows routers tocommunicate withother routers to updateand maintain therouting tablesExamples of routingprotocols that supportthe IP routed protocolare:RIP, IGRP,OSPF, BGP,and EIGRP. 245
  246. 246. 246
  247. 247. Routed ProtocolsProtocols used at the network layer that transfer data from one host to another acrossa router are called routed or routable protocols. The Internet Protocol (IP) and NovellsInternetwork Packet Exchange (IPX) are examples of routed protocols. Routers userouting protocols to exchange routing tables and share routing information. In otherwords, routing protocols enable routers to route routed protocols. 247
  248. 248. 248
  249. 249. Autonomous System An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined external routing policy. EGP Exterior Gateway Protocols are used for routing between Autonomous Systems AS 1000 AS 3000 IGP Interior Gateway Protocols are used for routing decisions AS 2000 within an Autonomous System. 249 Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)
  250. 250. Interior Gateway Protocol Exterior Gateway Interior Gateway Protocol (IGP) Protocol (EGP) (IGP) AS 1000 AS 3000 EGP EGP IGP EGP AS 2000 250 Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)
  251. 251. IGP and EGPAn autonomous system is a network or set of networks undercommon administrative control, such as the domain. 251
  252. 252. Categories of Routing ProtocolsMost routing algorithms can be classified into one of twocategories:• distance vector• link-stateThe distance vector routing approach determines the direction(vector) and distance to any link in the internetwork.The link-state approach, also called shortest path first,recreates the exact topology of the entire internetwork. 252
  253. 253. Distance VectorRouting Concepts 253
  254. 254. Distance Vector Routing (DVR) Destination Distance Routing table contains the addresses of destinations and the distance 1 of the way to this destination. 1 2 2 Hops 1 Hop 1 Hop Router A Router B Router C Router D Flow of routing information 254
  255. 255. Routing Tables Graphic 255
  256. 256. Distance VectorTopology Changes 256
  257. 257. Router Metric Components 257
  258. 258. Distance Vector Routing (DVR) Router A Router B Router C Router D 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 1 B 0 L 0 L 1 C 1 B 1 A 1 B 1 C 1 C 1 B L Locally connected 1 C 1 D 258
  259. 259. Distance Vector Routing (DVR) 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 1 B 0 L 0 L 1 C 1 B 1 A 1 B 1 C 2 B 1 C 1 B 2 C 2 B 1 C 1 D 2 C 2 C 2 B 0 L 0 L 0 L 0 L 0 L 0 L 0 L 0 L 1 B 0 L 0 L 1 C 1 B 1 A 1 B 1 C 2 B 1 C 1 B 2 C 2 B 1 C 1 D 2 C 3 B 2 C 2 B 3 C 259 Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)
  260. 260. RIPv1 Distance Vector Routing Protocol, classfulDistribution of Routing Tables via broadcast to adjacent routers Fig. 59 Properties of RIPv1 (TI1332EU02TI_0004 The Network Layer, 81) Only one kind of metric: Number of Hops Connections with different bandwidth can not be weighted Routing loops can occur -> bad convergence in case of a failure Count to infinity problem (infinity = 16) Maximum network size is limited by the number of hops 260
  261. 261. RIP Characteristics 261
  262. 262. RIP-1 permits only a Single Subnet Mask Port 1 RIP-1: RIP-1: Router A RIP-1: Port 2 262 Fig. 60 RIP-1 permits only a single subnet mask (TI1332EU02TI_0004 The Network Layer, 83)
  263. 263. Router ConfigurationThe router command starts a routing process.The network command is required because it enables therouting process to determine which interfaces participate in thesending and receiving of routing updates.An example of a routing configuration is:GAD(config)#router ripGAD(config-router)#network network numbers are based on the network classaddresses, not subnet addresses or individual host addresses. 263
  264. 264. Configuring RIP Example 264
  265. 265. Verifying RIP Configuration 265
  266. 266. The debug ip rip CommandMost of the RIPconfigurationerrors involve anincorrect networkstatement,discontiguoussubnets, or splithorizons. Onehighly effectivecommand forfinding RIPupdate issues isthe debug ip ripcommand. Thedebug ip ripcommanddisplays RIProuting updatesas they are sentand received. 266
  267. 267. Routing loopscan occur Problem: Routing Loopswheninconsistentrouting tablesare notupdated dueto slowconvergencein a changingnetwork. 267
  268. 268. Problem: Counting to Infinity 268
  269. 269. Solution: Define a Maximum 269
  270. 270. Solution: Split Horizon 270
  271. 271. Route PoisoningRoute poisoning is used by various distance vector protocols in order toovercome large routing loops and offer explicit information when a subnetor network is not accessible. This is usually accomplished by setting thehop count to one more than the maximum. 271
  272. 272. Triggered UpdatesNew routing tables are sent to neighboring routers on a regular basis.For example, RIP updates occur every 30 seconds.However a triggered update is sent immediately in response to somechange in the routing table.The router that detects a topology change immediately sends an updatemessage to adjacent routers that, in turn, generate triggered updatesnotifying their adjacent neighbors of the change.When a route fails, an update is sent immediately rather than waiting on theupdate timer to expire.Triggered updates, used in conjunction with route poisoning, ensure that allrouters know of failed routes before any holddown timers can expire. 272
  273. 273. Triggered Updates Graphic 273
  274. 274. Solution: Holddown Timers 274
  275. 275. IGRPInterior Gateway Routing Protocol (IGRP) is a proprietaryprotocol developed by Cisco.Some of the IGRP key design characteristics emphasizethe following:• It is a distance vector routing protocol.• Routing updates are broadcast every 90 seconds.• Bandwidth, load, delay and reliability are used to create a composite metric. 275
  276. 276. IGRP Stability FeaturesIGRP has a number of features that are designed to enhance its stability, such as:• Holddowns• Split horizons• Poison reverse updatesHolddownsHolddowns are used to prevent regular update messages from inappropriatelyreinstating a route that may not be up.Split horizonsSplit horizons are derived from the premise that it is usually not useful to sendinformation about a route back in the direction from which it came.Poison reverse updatesSplit horizons prevent routing loops between adjacent routers, but poison reverseupdates are necessary to defeat larger routing loops.Today, IGRP is showing its age, it lacks support for variable length subnet masks(VLSM). Rather than develop an IGRP version 2 to correct this problem, Cisco hasbuilt upon IGRPs legacy of success with Enhanced IGRP. 276
  277. 277. Configuring IGRP 277
  278. 278. Routing Metrics Graphics 278
  279. 279. Link State Concepts 279
  280. 280. Link State Topology Changes 280
  281. 281. Link State Routing (LSR)LSP: LSP:„My links to SPF „My links to R1 and R3 areR2 and R4 are up.up― Routing My link to R2 is down.― Table Router 1 Router 4 Router 2 Router 3 LSP: „My links to LSP: „My links to R1 and R3 are up, R2 and R4 are up.― my link to R4 is down.― state packet SPF... shortest path first 281
  282. 282. Link State Concerns 282
  283. 283. Link State Routing (LSR) 1 Router A Router C 4 2 2 Router E 1 4 Router B Router D Link State Database B-2 A-2 A-1 C-2 C-4 C-1 D-4 D-2 B-4 D-1 E-4 E-1 Router A Router B Router C Router D Router E A B C D B C A D D A E C B D C E E B A 283 E