PowerPoint PresentationCS 118 Spring 2014Network layerChapter 4: Network LayerTwo Key Network-Layer FunctionsSlide 7Connection setupSlide 11Slide 12“Virtual circuit” connectionVC implementationForwarding tableVirtual circuits: signaling protocolDatagram networksSlide 18Longest prefix matchingDatagram or VC network: why?Slide 21Router Architecture OverviewInput Port FunctionsThree types of switching fabricsSwitching Via MemorySwitching Via a BusSwitching Via An Interconnection NetworkSlide 32The Internet Network layerSlide 34IP datagram formatIP Fragmentation & ReassemblyIP Fragmentation and ReassemblySlide 38IP Addressing: introductionSubnetsSlide 41Slide 42IP addressing: CIDRIP addresses: how to get one?DHCP: Dynamic Host Configuration ProtocolDHCP client-server scenarioSlide 48Hierarchical addressing: route aggregationHierarchical addressing: more specific routesIP addressing: the last word...Network Layer 4-1Chapter 4Network LayerA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). 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Ross, All Rights ReservedTransport Layer 3-2CS 118 Spring 2014Chpt 4 - Section 4ANetwork Layer 4-3Network layertransport segment from sending to receiving host on sending side the net layer encapsulates TCP segments into datagramson rcving side, it delivers segments to transport layernetwork layer protocols in every host, routerrouter examines header fields in all IP datagrams passing through itapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalnetworkdata linkphysicalNetwork Layer 4-4Chapter 4: Network LayerChapter goals: understand network layer services:routingforwarding how a router worksadvanced topics: IPv6, mobilityinstantiation, implementation in the InternetNetwork Layer 4-6Two Key Network-Layer Functionsforwarding: move packets from router’s input to appropriate router outputrouting: compute the route that must be taken by packets from source to dest. routing algorithmsanalogy:routing: planning trip from source to destforwarding: moving the “actual” bits to the next nodeNetwork Layer 4-71230111value in arrivingpacket’s headerrouting algorithmlocal forwarding tableheader valueoutput link01000101011110013221Routing precedes forwardingNetwork Layer 4-8Connection setup3rd important function in some network architectures:ATM, frame relay, X.25before datagrams flow, two end hosts and intervening routers establish virtual connectionrouters get involvednetwork vs transport layer connection service:network: between two hosts (may also involve intervening routers in case of VCs)transport: between two processesNetwork Layer 4-11Chapter 4: Network Layer4. 1 Introduction4.2 Virtual circuit and datagram networks4.3 What’s inside a router4.4 IP: Internet ProtocolDatagram formatIPv4 addressingICMPIPv64.5 Routing algorithmsLink stateDistance VectorHierarchical routing4.6 Routing in the InternetRIPOSPFBGP4.7 Broadcast and multicast routingNetwork Layer 4-12Datagram network: connectionless serviceVirtual Circuit network: connection serviceNetwork Layer 4-13“Virtual circuit” connectioncall setup for each connection before data can floweach packet carries VC identifier every intermediate router maintains state of the connectionresources (bandwidth, buffers) may be allocated to the VC at each intermediate routersource-to-dest connection is set up much like a telephone circuitNetwork Layer 4-14VC implementationVC defined by 3 entities:1. path from source to destination2. VC numbers, one for each link along path3. forwarding table entries in routers along pathpacket carries VC number (instead of dest address)VC number changed at each link.Network Layer 4-15Forwarding table122232123VC numberinterfacenumberIncoming interface Incoming VC # Outgoing interface Outgoing VC #1 12 3 222 63 1 18 3 7 2 171 97 3 87… … … …Forwarding table inrouter A:ANetwork Layer 4-16Virtual circuits: signaling protocolused to setup, maintain teardown VCapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysical1. Initiate call2. incoming call3. Accept call4. Call connected5. Data flow begins6. Receive dataNetwork Layer 4-17Datagram networksno call setup at network layerno notion of connection: packets may take “alternate” pathsrouters: no state about end-to-end connectionspackets forwarded using destination host addressapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysical1. Send data2. Receive dataNetwork Layer 4-18Forwarding table Destination Address (32 bits) Link Interface 11001000 00010111 00010000 00000000 through 0 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 1 11001000 00010111 00011000 11111111 11001000 00010111 00011001 00000000 through 2 11001000 00010111 00011111 11111111 otherwise 34 billion possible entriesNetwork Layer 4-19Longest prefix matching Prefix Match Link Interface 11001000 00010111 00010XXX XXXXXXXX 0 11001000 00010111 00011000 XXXXXXXX 1 11001000 00010111 00011XXX XXXXXXXX 2 otherwise 3DA: 11001000
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