agenda week 1: internet history and basic concepts week 2: routing vs. switching week 3:...
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Agenda Week 1: Internet History and Basic Concepts
Week 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
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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
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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
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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?
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Packet Protocol Families
• ATM
• IP
• IPX
• Appletalk
• DECNET
• XNS
• PUP
• BNA
• SNA
• OSI
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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 ?
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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
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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
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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)
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But wait! There’s more…Ethernet Frame Formats
• Ethernet II
• IEEE 802.3
• IEEE 802.2 (802.3 + LLC)
• Ethernet SNAP
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Mapping Layers to Boxes
• Layer 1 > Repeaters
• Layer 2 > Smart Hubs, Bridges/Switches
• Layer 3 > Routers
• So what’s a “Layer 3 Switch” ??
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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?
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What’s Really on the Wire?
• MAC, LSAP, & Network Addresses
• Ethernet framing
• Layering and encapsulation example
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Network Addresses/Identifiers
• MAC
• LSAP
• Network
• Port
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Address Properties
• Global or context sensitive?
• Identifier or Locator?
• Locators: topological or geographic?
• Hierarchical or flat?
• Unicast or multicast or broadcast?
• How assigned?
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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
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Ethernet/IP/TCP Example8 Preamble/SFD6 Destination Address6 Source Address2 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 Port2 Destination Port4 Sequence Number4 ACK Number2 Offset, Reserved bits, Flags2 Receive Window Size2 Checksum2 Urgent Pointer? Options/Padding
<<< DATA >>>4 FCS
TCP Header
IP Header
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Inside the Boxes
• Connecting Different Kinds of Links
• What goes on Inside the Box
• Routing Approaches
• Packet Classifying/Labeling
• The Key Debate
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Connecting Different Kinds of LinksCan we handle differences in...
• Media Type ?
• Data Link Type ?
• Frame Format ?
• Max Frame Size ?
• Speed ?
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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
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What goes on Inside the Box -2
• Forwarding
• Routing
• Labeling?
• Error Handling
• Congestion control
• Management
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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)
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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
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The Key Debate
“Switch when you can, route when you must”
vs.
“Routers are your friend”
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Switching & Routing Tradeoffs
SWITCHES ROUTERSTraffic isolation + +Broadcast isolation - +Address conflict isolation - +Multicast support ? +COS/QOS support ? +Loadsharing uplinks - +Configuration complexity + -Internal complexity + -Protocol independence + -Cost + -
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Services, Addresses, & Layers
• Layering Questions
• Services by Address
• Layer 3 Switching
• Fast IP (Cut Thru) Switching
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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
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Services based on Layer 2 addresses
• Frame forwarding
• Learning and Spanning tree routing
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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
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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
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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
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IP Switching
• Minimum use of Routers
• Most packets “cut thru” to L2 path
• Packet classification strategies vary
• Not just for ATM L2
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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.
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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
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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