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Agenda

Agenda.

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Agenda

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  1. Agenda Week 1: Internet History and Basic ConceptsWeek 2: Routing vs. SwitchingWeek 3: Architecture and Topology TrendsWeek 4: Multimedia (QoS, CoS, multicast)Week 5: ATM vs. IPWeek 6: Routing part 1 (Intro, RIP, OSPF)Week 7: Routing part 2 (BGP, state of the Internet)Week 8: TBD --Guest lecture(s) Week 9: Failure Modes and Fault DiagnosisWeek 10: Product evaluation criteria

  2. Week 2: Switching vs. Routing • Network Ingredients • What’s Really on the Wire? • Inside the Boxes • Switching & Routing Tradeoffs • Services, Addresses, & Layers • Those New-Fangled Hybrids

  3. Network Ingredientsbits, boxes, wires and waves… • Switching Techniques • Protocol Families • The Network Core: Layers 1-3 • Data Link Elements • Data Link Families • Mapping Layers to Boxes • VLANs

  4. Switching Techniques • Circuit (SDM or TDM or FDM) • Establish fixed end-to-end connection • Message (Store-and-forward) • No longer used at layers 2-3 • Packet (Frame, FPS, Cell) • Datagram: connectionless, StatMuxed channel • Virtual Circuit: connection-oriented, PVC/SVC • (Virtual) Circuits over Packets? • Packets over (Virtual) Circuits? • Multicast vs. (Virtual) Circuits?

  5. ATM IP IPX Appletalk DECNET XNS PUP BNA SNA OSI Packet Protocol Families

  6. The Network Core: Layers 1-3 3 Network • Key element: global addresses 2 Data Link • Logical Link Control (LLC) • Media Access Control (MAC) 1 Physical/Media (PHY) • e.g. UTP, Coax, Fiber, Wireless • Do core elements care about layers >3 ?

  7. Data Link Elementsala IEEE 802 and ISO 8802 • Topology • Bus, Ring, Star/Tree… Mesh, Point-to-Point • Logical Link Control (LLC) • Connection, Connectionless, Connectionless w/ACKs • Media Access Control (MAC) • Contention, Reservation, Round robin • Addressing Scheme

  8. Data Link Choices • 802.3 Ethernet • 802.4 Token Bus • 802.5 Token Ring • 802.6 DQDB • 802.7 Broadband • 802.11 Wireless • 802.12 DPAM (100VG) • 802.14 CATV • FDDI • HIPPI • Fibre Channel • SONET • ARCnet, Starlan, Lattisnet

  9. Choosing Ethernet? Welcome to the World of 802.3 • 10Base5, 10Base2, 10Broad36, 10Base-T, 10Base-F… (802.3-1996) • 100BaseTX, 100BaseT4, 100BaseT2, 100BaseFX… (802.3u, y, aa) • 1000BaseCX, LX, SX, T (802.3z, ab) • Full Duplex, Flow Control (802.3x)

  10. But wait! There’s more…Ethernet Frame Formats • Ethernet II • IEEE 802.3 • IEEE 802.2 (802.3 + LLC) • Ethernet SNAP

  11. Mapping Layers to Boxes • Layer 1 > Repeaters • Layer 2 > Smart Hubs, Bridges/Switches • Layer 3 > Routers • So what’s a “Layer 3 Switch” ??

  12. VLANs • Provide logical grouping of ports/hosts • Independent of physical topology • Goals: • Avoid re-addressing when hosts move • Avoid traversing routers unnecessarily • Can provide foundation for multicast • VLAN Identifiers in 802.1Q • 4096 values • New field in frame header • Based on port, MAC address, or ?? • What about adding VID to max size frames?

  13. What’s Really on the Wire? • MAC, LSAP, & Network Addresses • Ethernet framing • Layering and encapsulation example

  14. Network Addresses/Identifiers • MAC • LSAP • Network • Port

  15. Address Properties • Global or context sensitive? • Identifier or Locator? • Locators: topological or geographic? • Hierarchical or flat? • Unicast or multicast or broadcast? • How assigned?

  16. Ethernet II 8 Preamble/SFD 6 Destination Address 6 Source Address 2 Type 46-1500 Data 4 FCS 802.3 8 Preamble/SFD 6 Destination Address 6 Source Address 2 Length (max 5DC) 46-1500 Data 4 FCS Two Ethernet Frame Layouts

  17. Ethernet/IP/TCP Example 8 Preamble/SFD 6 Destination Address 6 Source Address 2 Type 1 Version & Header Length 1 Type of Service 2 Total Datagram Length 2 Identification 2 Flags & Fragment Offset 1 Time to Live 1 Protocol 2 Header Checksum 4 Source Address 4 Destination Address ? Options/Padding 2 Source Port 2 Destination Port 4 Sequence Number 4 ACK Number 2 Offset, Reserved bits, Flags 2 Receive Window Size 2 Checksum 2 Urgent Pointer ? Options/Padding <<< DATA >>> 4 FCS IP Header TCP Header

  18. Inside the Boxes • Connecting Different Kinds of Links • What goes on Inside the Box • Routing Approaches • Packet Classifying/Labeling • The Key Debate

  19. Connecting Different Kinds of LinksCan we handle differences in... • Media Type ? • Data Link Type ? • Frame Format ? • Max Frame Size ? • Speed ?

  20. What goes on Inside the Box? • Given: Incoming Packet + Internal State • Result: Forwarding Decision + New State • State: configuration, routing/forwarding database, buffers, buffer allocations, etc

  21. What goes on Inside the Box -2 • Forwarding • Routing • Labeling? • Error Handling • Congestion control • Management

  22. Routing Approaches • Layer 2 • Source routing • Address learning • Protocol (Spanning Tree, 802.1p, Q) • Layer 3 • Source routing • Learning + Sniffing • Protocol (RIP, OSPF, IS-IS, P-NNI)

  23. Packet Classifying/Labeling • Dynamic, based on examining each packet • Dynamic, based on real-time flow analysis • Topological, based on routing info • Static, based on manual configuration

  24. The Key Debate “Switch when you can, route when you must” vs. “Routers are your friend”

  25. SWITCHES ROUTERS Traffic isolation + + Broadcast isolation - + Address conflict isolation - + Multicast support ? + COS/QOS support ? + Loadsharing uplinks - + Configuration complexity + - Internal complexity + - Protocol independence + - Cost + - Switching & Routing Tradeoffs

  26. Services, Addresses, & Layers • Layering Questions • Services by Address • Layer 3 Switching • Fast IP (Cut Thru) Switching

  27. Layering Questions • Do core devices care about layers >3 ? • Generally no, but... • What about performance? • Impact of speed mismatches on tcp vs. udp • Do Layer 2 devices care about layers >2 ? • By definition , no, but... • Consider multi-protocol QOS • Multiple Layer 3 protocols force more complexity into Layer 2

  28. Services based on Layer 2 addresses • Frame forwarding • Learning and Spanning tree routing

  29. Services based on Layer 3 addresses/ports • IP packet forwarding • IP policy or destination-based routing • Constraining IP address conflicts • Multicast • COS/QOS • Loadsharing • Broadcast isolation • Accounting

  30. Layer 3 services that are showing up in switches: • Multicast support (IGMP vs. 802.1Q) • COS/QOS? (RSVP vs. 802.1p) • Fast IP (IPX) forwarding

  31. Layer 3 “Switching” • Goal: IP packet forwarding with price/performance of Layer 2 switches • Limited flexibility • IP (and maybe IPX) only • No policy routing, accounting

  32. IP Switching • Minimum use of Routers • Most packets “cut thru” to L2 path • Packet classification strategies vary • Not just for ATM L2

  33. Where do VLANs fit? • Enable strange/wonderful topologies • Gave us cute terms like “One Arm Router” • Introducing Semi-permeable L2 links: • Use VLANs to limit broadcasts • Normally VLANs connected by routers • Can permit L2 cut-thru between VLANsjust for unicast packets.

  34. Those New-Fangled Boxes • Ipsilon’s IP Switching • 3Com’s Fast IP Architecture • IBM’s ARIS • Bay’s Layer 3 switch • Cisco’s Tag Switching • Rapid City, et al

  35. More Gray’s Networking Nuggets • Zero and Two are my favorite numbers • Managing many of the same thing is easier than managing many different things • One man’s floor is another man’s ceilingProtocol encapsulation is a Good Thing • Self-describing data is the key to an orderly universe

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