1. Agenda Week 1: Internet History and Basic Concepts Week 2: Routing vs. Switching Week 3: Architecture and Topology Trends Week 4: Multimedia (QoS, CoS, multicast) Week 5: ATM vs. IP Week 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 Diagnosis Week 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 Ingredients bits, 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. Packet Protocol Families ATM IP IPX Appletalk DECNET XNS PUP BNA SNA OSI

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 Elements ala 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. Two Ethernet Frame Layouts 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

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 >> 4 FCS TCP Header IP 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 Links Can 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. Switching & Routing Tradeoffs SWITCHES ROUTERS Traffic isolation++ Broadcast isolation-+ Address conflict isolation-+ Multicast support?+ COS/QOS support?+ Loadsharing uplinks-+ Configuration complexity+- Internal complexity+- Protocol independence+- Cost+-

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 VLANs just 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 ceiling Protocol encapsulation is a Good Thing Self-describing data is the key to an orderly universe