chapter_15_internetwork_protocols

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(Internetwork protocols (chapter 15

اسلاید 1: William Stallings Data and Computer CommunicationsChapter 15Internetwork Protocols

اسلاید 2: Internetworking Terms (1)Communications NetworkFacility that provides data transfer serviceAn internetCollection of communications networks interconnected by bridges and/or routersThe Internet - note upper case IThe global collection of thousands of individual machines and networksIntranetCorporate internet operating within the organizationUses Internet (TCP/IP and http)technology to deliver documents and resources

اسلاید 3: Internetworking Terms (2)End System (ES)Device attached to one of the networks of an internetSupports end-user applications or servicesIntermediate System (IS)Device used to connect two networksPermits communication between end systems attached to different networks

اسلاید 4: Internetworking Terms (3)BridgeIS used to connect two LANs using similar LAN protocolsAddress filter passing on packets to the required network onlyOSI layer 2 (Data Link)RouterConnects two (possibly dissimilar) networksUses internet protocol present in each router and end systemOSI Layer 3 (Network)

اسلاید 5: Internetworking Protocols

اسلاید 6: Requirements of InternetworkingLink between networksMinimum physical and link layerRouting and delivery of data between processes on different networksAccounting services and status infoIndependent of network architectures

اسلاید 7: Network Architecture FeaturesAddressingPacket sizeAccess mechanismTimeoutsError recoveryStatus reportingRoutingUser access controlConnection based or connectionless

اسلاید 8: Architectural ApproachesConnection orientedConnectionless

اسلاید 9: Connection OrientedAssume that each network is connection orientedIS connect two or more networksIS appear as DTE to each networkLogical connection set up between DTEsConcatenation of logical connections across networksIndividual network virtual circuits joined by ISMay require enhancement of local network services802, FDDI are datagram services

اسلاید 10: Connection Oriented IS FunctionsRelayingRoutinge.g. X.75 used to interconnect X.25 packet switched networksConnection oriented not often used(IP dominant)

اسلاید 11: Connectionless OperationCorresponds to datagram mechanism in packet switched networkEach NPDU treated separatelyNetwork layer protocol common to all DTEs and routersKnown generically as the internet protocolInternet ProtocolOne such internet protocol developed for ARPANETRFC 791 (Get it and study it)Lower layer protocol needed to access particular network

اسلاید 12: Connectionless InternetworkingAdvantagesFlexibilityRobustNo unnecessary overheadUnreliableNot guaranteed deliveryNot guaranteed order of deliveryPackets can take different routesReliability is responsibility of next layer up (e.g. TCP)

اسلاید 13: IP Operation

اسلاید 14: Design IssuesRoutingDatagram lifetimeFragmentation and re-assemblyError controlFlow control

اسلاید 15: RoutingEnd systems and routers maintain routing tablesIndicate next router to which datagram should be sentStatic May contain alternative routesDynamicFlexible response to congestion and errorsSource routingSource specifies route as sequential list of routers to be followedSecurityPriorityRoute recording

اسلاید 16: Datagram LifetimeDatagrams could loop indefinitelyConsumes resourcesTransport protocol may need upper bound on datagram lifeDatagram marked with lifetime Time To Live field in IPOnce lifetime expires, datagram discarded (not forwarded)Hop countDecrement time to live on passing through a each routerTime countNeed to know how long since last router(Aside: compare with Logan’s Run)

اسلاید 17: Fragmentation and Re-assemblyDifferent packet sizesWhen to re-assembleAt destinationResults in packets getting smaller as data traverses internetIntermediate re-assemblyNeed large buffers at routersBuffers may fill with fragmentsAll fragments must go through same routerInhibits dynamic routing

اسلاید 18: IP Fragmentation (1)IP re-assembles at destination onlyUses fields in headerData Unit Identifier (ID)Identifies end system originated datagramSource and destination addressProtocol layer generating data (e.g. TCP)Identification supplied by that layerData lengthLength of user data in octets

اسلاید 19: IP Fragmentation (2)OffsetPosition of fragment of user data in original datagramIn multiples of 64 bits (8 octets)More flagIndicates that this is not the last fragment

اسلاید 20: Fragmentation Example

اسلاید 21: Dealing with FailureRe-assembly may fail if some fragments get lostNeed to detect failureRe-assembly time outAssigned to first fragment to arriveIf timeout expires before all fragments arrive, discard partial dataUse packet lifetime (time to live in IP)If time to live runs out, kill partial data

اسلاید 22: Error ControlNot guaranteed deliveryRouter should attempt to inform source if packet discarded e.g. for time to live expiringSource may modify transmission strategyMay inform high layer protocolDatagram identification needed(Look up ICMP)

اسلاید 23: Flow ControlAllows routers and/or stations to limit rate of incoming dataLimited in connectionless systemsSend flow control packetsRequesting reduced flowe.g. ICMP

اسلاید 24: Internet Protocol (IP)Part of TCP/IPUsed by the InternetSpecifies interface with higher layere.g. TCPSpecifies protocol format and mechanisms

اسلاید 25: IP ServicesPrimitivesFunctions to be performedForm of primitive implementation dependente.g. subroutine callSendRequest transmission of data unitDeliverNotify user of arrival of data unitParametersUsed to pass data and control info

اسلاید 26: Parameters (1)Source addressDestination addressProtocolRecipient e.g. TCPType of ServiceSpecify treatment of data unit during transmission through networksIdentificationSource, destination address and user protocolUniquely identifies PDUNeeded for re-assembly and error reportingSend only

اسلاید 27: Parameters (2)Don’t fragment indicatorCan IP fragment dataIf not, may not be possible to deliverSend onlyTime to liveSend onlData lengthOption dataUser data

اسلاید 28: Type of ServicePrecedence8 levelsReliabilityNormal or highDelayNormal or lowThroughputNormal or high

اسلاید 29: OptionsSecuritySource routingRoute recordingStream identificationTimestamping

اسلاید 30: IP Protocol

اسلاید 31: Header Fields (1)VersionCurrently 4IP v6 - see laterInternet header lengthIn 32 bit wordsIncluding optionsType of serviceTotal lengthOf datagram, in octets

اسلاید 32: Header Fields (2)IdentificationSequence numberUsed with addresses and user protocol to identify datagram uniquelyFlagsMore bitDon’t fragmentFragmentation offsetTime to liveProtocolNext higher layer to receive data field at destination

اسلاید 33: Header Fields (3)Header checksumReverified and recomputed at each router16 bit ones complement sum of all 16 bit words in headerSet to zero during calculationSource addressDestination addressOptionsPaddingTo fill to multiple of 32 bits long

اسلاید 34: Data FieldCarries user data from next layer upInteger multiple of 8 bits long (octet)Max length of datagram (header plus data) 65,535 octets

اسلاید 35: IP Addresses - Class A32 bit global internet addressNetwork part and host partClass AStart with binary 0All 0 reserved01111111 (127) reserved for loopbackRange 1.x.x.x to 126.x.x.xAll allocated

اسلاید 36: IP Addresses - Class BStart 10Range 128.x.x.x to 191.x.x.xSecond Octet also included in network address214 = 16,384 class B addressesAll allocated

اسلاید 37: IP Addresses - Class CStart 110Range 192.x.x.x to 223.x.x.xSecond and third octet also part of network address221 = 2,097,152 addressesNearly all allocatedSee IPv6

اسلاید 38: Subnets and Subnet MasksAllow arbitrary complexity of internetworked LANs within organizationInsulate overall internet from growth of network numbers and routing complexitySite looks to rest of internet like single networkEach LAN assigned subnet numberHost portion of address partitioned into subnet number and host numberLocal routers route within subnetted networkSubnet mask indicates which bits are subnet number and which are host number

اسلاید 39: Routing Using Subnets

اسلاید 40: ICMPInternet Control Message ProtocolRFC 792 (get it and study it)Transfer of (control) messages from routers and hosts to hostsFeedback about problemse.g. time to live expiredEncapsulated in IP datagramNot reliable

اسلاید 41: ICMP Message Formats

اسلاید 42: IP v6 - Version NumberIP v 1-3 defined and replacedIP v4 - current versionIP v5 - streams protocolIP v6 - replacement for IP v4During development it was called IPng Next Generation

اسلاید 43: Why Change IP?Address space exhaustionTwo level addressing (network and host) wastes spaceNetwork addresses used even if not connected to InternetGrowth of networks and the InternetExtended use of TCP/IPSingle address per hostRequirements for new types of service

اسلاید 44: IPv6 RFCs1752 - Recommendations for the IP Next Generation Protocol2460 - Overall specification2373 - addressing structureothers (find them)

اسلاید 45: Expanded address space128 bitImproved option mechanismSeparate optional headers between IPv6 header and transport layer headerMost are not examined by intermediate routesImproved speed and simplified router processingEasier to extend optionsAddress autoconfigurationDynamic assignment of addresses

اسلاید 46: IPv6 Enhancements (2)Increased addressing flexibilityAnycast - delivered to one of a set of nodesImproved scalability of multicast addressesSupport for resource allocationReplaces type of serviceLabeling of packets to particular traffic flowAllows special handlinge.g. real time video

اسلاید 47: Structure

اسلاید 48: Extension HeadersHop-by-Hop OptionsRequire processing at each routerRoutingSimilar to v4 source routingFragmentAuthenticationEncapsulating security payloadDestination optionsFor destination node

اسلاید 49: IP v6 Header

اسلاید 50: IP v6 Header Fields (1)Version6Traffic ClassClasses or priorities of packetStill under developmentSee RFC 2460Flow LabelUsed by hosts requesting special handlingPayload lengthIncludes all extension headers plus user data

اسلاید 51: IP v6 Header Fields (2)Next HeaderIdentifies type of headerExtension or next layer upSource AddressDestination address

اسلاید 52: IPv6 Addresses128 bits longAssigned to interfaceSingle interface may have multiple unicast addressesThree types of address

اسلاید 53: Types of addressUnicastSingle interfaceAnycastSet of interfaces (typically different nodes)Delivered to any one interfacethe “nearest”MulticastSet of interfacesDelivered to all interfaces identified

اسلاید 54: Hop-by-Hop OptionsNext headerHeader extension lengthOptionsJumbo payloadOver 216 = 65,535 octetsRouter alertTells the router that the contents of this packet is of interest to the routerProvides support for RSPV (chapter 16)

اسلاید 55: Fragmentation HeaderFragmentation only allowed at sourceNo fragmentation at intermediate routersNode must perform path discovery to find smallest MTU of intermediate networksSource fragments to match MTUOtherwise limit to 1280 octets

اسلاید 56: Fragmentation Header FieldsNext HeaderReservedFragmentation offsetReservedMore flagIdentification

اسلاید 57: Routing HeaderList of one or more intermediate nodes to be visitedNext HeaderHeader extension lengthRouting typeSegments lefti.e. number of nodes still to be visited

اسلاید 58: Destination OptionsSame format as Hop-by-Hop options header

اسلاید 59: MulticastingAddresses that refer to group of hosts on one or more networksUsesMultimedia “broadcast”TeleconferencingDatabaseDistributed computingReal time workgroups

اسلاید 60: Example Config

اسلاید 61: Broadcast and Multiple UnicastBroadcast a copy of packet to each networkRequires 13 copies of packetMultiple UnicastSend packet only to networks that have hosts in group11 packets

اسلاید 62: True MulticastDetermine least cost path to each network that has host in groupGives spanning tree configuration containing networks with group membersTransmit single packet along spanning treeRouters replicate packets at branch points of spanning tree8 packets required

اسلاید 63: Multicast Example

اسلاید 64: Requirements for Multicasting (1)Router may have to forward more than one copy of packetConvention needed to identify multicast addressesIPv4 - Class D - start 1110IPv6 - 8 bit prefix, all 1, 4 bit flags field, 4 bit scope field, 112 bit group identifierNodes must translate between IP multicast addresses and list of networks containing group membersRouter must translate between IP multicast address and network multicast address

اسلاید 65: Requirements for Multicasting (2)Mechanism required for hosts to join and leave multicast groupRouters must exchange infoWhich networks include members of given groupSufficient info to work out shortest path to each networkRouting algorithm to work out shortest pathRouters must determine routing paths based on source and destination addresses

اسلاید 66: IGMPInternet Group Management ProtocolRFC 1112Host and router exchange of multicast group infoUse broadcast LAN to transfer info among multiple hosts and routers

اسلاید 67: IGMP Format

اسلاید 68: IGMP FieldsVersion1Type1 - query sent by routerO - report sent by hostChecksumGroup addressZero in request messageValid group address in report message

اسلاید 69: IGMP OperationTo join a group, hosts sends report messageGroup address of group to joinIn IP datagram to same multicast destination addressAll hosts in group receive messageRouters listen to all multicast addresses to hear all reportsRouters periodically issue request messageSent to all-hosts multicast addressHost that want to stay in groups must read all-hosts messages and respond with report for each group it is in

اسلاید 70: Group Membership in IPv6Function of IGMP included in ICMP v6New group membership termination message to allow host to leave group

اسلاید 71: Required ReadingStallings chapter 15Comer, S. Internetworking with TCP/IP, volume 1, Prentice-HallAll RFCs mentioned plus any others connected with these topicsLoads of Web sites on TCP/IP and IP version 6.

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