2.8.networking-overview - Networking Overview CS 161...

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1 Networking Overview CS 161 - Computer Security Profs. Vern Paxson & David Wagner TAs: John Bethencourt, Erika Chin, Matthew Finifter, Cynthia Sturton, Joel Weinberger http://inst.eecs.berkeley.edu/~cs161/ Feb 8, 2010
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2 Focus For Today ʼ s Lecture Sufficient background in networking to then explore security issues in next 4 lectures Networking = the Internet Complex topic with many facets We will omit concepts/details that aren’t very security- relevant We’ll mainly look at IP , TCP , DNS and DHCP Networking is full of abstractions Goal is for you to develop apt mental models / analogies ASK questions when things are unclear o (but we may skip if not ultimately relevant for security, or postpone if question itself is directly about security)
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3 Key Concept #1: Dumb Network Internet design: interior nodes (“routers”) have no knowledge* of ongoing connections going through them Not: how you picture the telephone system works Which internally tracks all of the active voice calls Instead: the postal system! Each Internet message (“packet”) self-contained Interior “routers” look at destination address to forward If you want smarts, build it “end-to-end” Buys simplicity & robustness at the cost of shifting complexity into end systems * Today’s Internet is full of hacks that violate this
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4 Key Concept #2: Layering Internet design is strongly partitioned into layers Each layer relies on services provided by next layer below … … and provides services to layer above it • Analogy: Consider structure of an application you’ve written and the “services” each layer relies on / provides Code You Write Run-Time Library System Calls Device Drivers Voltage Levels / Magnetic Domains } Fully isolated from user programs
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5 Internet Layering (“Protocol Stack”) Application Transport (Inter)Network Link Physical 7 4 3 2 1
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6 Layer 1: Physical Layer Application Transport (Inter)Network Link Physical 7 4 3 2 1 Encoding bits to send them over a single physical link e.g. patterns of voltage levels / photon intensities / RF modulation
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7 Layer 2: Link Layer Application Transport (Inter)Network Link Physical 7 4 3 2 1 Framing and transmission of a collection of bits into individual messages sent across a single “subnetwork” (one physical technology) Might involve multiple physical links (e.g., modern Ethernet) Often technology supports broadcast transmission ( every “node” connected to subnet receives)
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8 Layer 3: (Inter)Network Layer Application Transport (Inter)Network Link Physical 7 4 3 2 1 Bridges multiple subnets to provide end-to-end internet connectivity between nodes Provides global addressing Works across different link technologies } Different for each Internet “hop”
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9 Layer 4: Transport Layer Application Transport (Inter)Network Link
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