Transcript Week 2: Routing vs. Switching

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
Week 2: Switching vs. Routing
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Network Ingredients
What’s Really on the Wire?
Inside the Boxes
Switching & Routing Tradeoffs
Services, Addresses, & Layers
Those New-Fangled Hybrids
Network Ingredients
bits, boxes, wires and waves…
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Switching Techniques
Protocol Families
The Network Core: Layers 1-3
Data Link Elements
Data Link Families
Mapping Layers to Boxes
VLANs
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?
Packet Protocol Families
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ATM
IP
IPX
Appletalk
DECNET
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XNS
PUP
BNA
SNA
OSI
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 ?
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
Data Link Choices
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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
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)
But wait! There’s more…
Ethernet Frame Formats
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Ethernet II
IEEE 802.3
IEEE 802.2 (802.3 + LLC)
Ethernet SNAP
Mapping Layers to Boxes
• Layer 1 > Repeaters
• Layer 2 > Smart Hubs, Bridges/Switches
• Layer 3 > Routers
• So what’s a “Layer 3 Switch” ??
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
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4096 values
New field in frame header
Based on port, MAC address, or ??
What about adding VID to max size frames?
What’s Really on the Wire?
• MAC, LSAP, & Network Addresses
• Ethernet framing
• Layering and encapsulation example
Network Addresses/Identifiers
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MAC
LSAP
Network
Port
Address Properties
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Global or context sensitive?
Identifier or Locator?
Locators: topological or geographic?
Hierarchical or flat?
Unicast or multicast or broadcast?
How assigned?
Two Ethernet Frame Layouts
• Ethernet II
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8 Preamble/SFD
6 Destination Address
6 Source Address
2 Type
46-1500 Data
4 FCS
• 802.3
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8 Preamble/SFD
6 Destination Address
6 Source Address
2 Length (max 5DC)
46-1500 Data
4 FCS
Ethernet/IP/TCP Example
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Preamble/SFD
Destination Address
Source Address
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
Inside the Boxes
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Connecting Different Kinds of Links
What goes on Inside the Box
Routing Approaches
Packet Classifying/Labeling
The Key Debate
Connecting Different Kinds of Links
Can we handle differences in...
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Media Type ?
Data Link Type ?
Frame Format ?
Max Frame Size ?
Speed ?
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
What goes on Inside the Box -2
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Forwarding
Routing
Labeling?
Error Handling
Congestion control
Management
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)
Packet Classifying/Labeling
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Dynamic, based on examining each packet
Dynamic, based on real-time flow analysis
Topological, based on routing info
Static, based on manual configuration
The Key Debate
“Switch when you can, route when you must”
vs.
“Routers are your friend”
Switching & Routing Tradeoffs
SWITCHES
Traffic isolation
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Broadcast isolation
Address conflict isolation
Multicast support
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COS/QOS support
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Loadsharing uplinks
Configuration complexity
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Internal complexity
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Protocol independence
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Cost
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ROUTERS
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Services, Addresses, & Layers
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Layering Questions
Services by Address
Layer 3 Switching
Fast IP (Cut Thru) Switching
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
Services based on Layer 2
addresses
• Frame forwarding
• Learning and Spanning tree routing
Services based on Layer 3
addresses/ports
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IP packet forwarding
IP policy or destination-based routing
Constraining IP address conflicts
Multicast
COS/QOS
Loadsharing
Broadcast isolation
Accounting
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
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
IP Switching
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Minimum use of Routers
Most packets “cut thru” to L2 path
Packet classification strategies vary
Not just for ATM L2
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.
Those New-Fangled Boxes
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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
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