08-IP - Designing IP EE122 Fall 2011 Scott Shenker

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1 Designing IP EE122 Fall 2011 Scott Shenker http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks to Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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2 Today’s Lecture is a Transition From heady principles… ...to packet headers From essentials… …to esoterica From fundamentals… …to no-fun-at-all
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Today’s (Boring) Topics • Design of IP • Comparison with IPv6 • Quick Security Analysis • Introduction to IP Addressing But first, a chance to grill Shaddi about Project 1 3
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Questions about Project 1 4
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The Design of IP 5
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6 What is designing a protocol? • Specifying the syntax of its messages – Format • Specifying their semantics – Meaning – Responses
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What is Designing IP? • Syntax: format of packet – Nontrivial part: packet “header” – Rest is opaque payload (why opaque?) • Semantics: meaning of header fields – Required processing 7 Header Opaque Payload
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Packet Header as Interface • Think of packet header as interface – Only way of passing information from packet to switch • Designing interfaces: – What task are you trying to perform? – What information do you need to accomplish it? • Header reflects information needed for basic tasks 8
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In-Class Exercise • Five minutes to design the IPv7 packet header Do not look at book, or otherwise copy IPv4 or IPv6 Do work in groups • Goal not to get right answer, but to think about: – What tasks are involved? – How can a packet header accomplish it? • Note: IPv4 is not a great model – Try to do better! 9
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I’ll Take Two or Three Answers • You tell me your: – Task list – Corresponding information in header And any deep insights about architecture? TAs will write on board We will compare and discuss Provide useful background for rest of lecture 10
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What Tasks Do We Need to Do? • Read packet correctly • Get packet to the destination • Get responses to the packet back to source • Carry data • Tell host what to do with packet once arrived • Specify any special network handling of the packet • Deal with problems that arise along the path 11
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Reading Packet Correctly • Where does header end? • Where does packet end? • What version of IP? Why is this so important? 12
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Getting to the Destination • Provide destination address (duh!) • Should this be location or identifier? – And what’s the difference? • If a host moves, should its address change? – If not, how can you build scalable Internet? – If so, then what good is an address for identification? 13
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Getting Response Back to Source • Source address (duh!) 14
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Carry Data • Payload (duh!) 15
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Telling Dest’n How to Process Packet • Indicate which protocols should handle packet • What layer should this protocol be in?
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08-IP - Designing IP EE122 Fall 2011 Scott Shenker

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