02-16-2010-answers - CS 161 Computer Security Spring 2010...

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Unformatted text preview: CS 161 Computer Security Spring 2010 Paxson/Wagner Discussion 4 February 16, 2010 1. Protocol Layers At which network layer does each of the following operate (physical, link, network, trans- port, or application)? • Ethernet (Link - 2) • SMTP (App - 7) • SYN packet (Transport - 4) • UDP (Transport - 4) • Fiber optics (Physical - 1) • FTP (App - 7) • DNS request (App - 7) • BitTorrent (App - 7) • TTL field (Network - 3) • Hub (Physical - 1) • (Network - 3) • 802.11n WiFi (Physical, Link - 1, 2) 2. TCP and UDP Transmission control protocol (TCP) and user datagram protocol (UDP) are two of the primary protocols of the Internet protocol suite. (a) How do TCP and UDP relate to IP (Internet protocol)? Which of these protocols are encapsulated within (or layered atop) one another? Could all three be used simultaneously? (b) What are the differences between TCP and UDP? Which is considered “best effort”? What does that mean? (c) Which is easier to spoof, and why? Answer: (a) TCP and UDP both exist within the transport layer, which is one layer above IP (network layer). Either can be encapsulated in IP, referred to as TCP/IP and UDP/IP. TCP and UDP are alternatives; neither would normally be encapsulated within the other. (b) TCP provides a connection-oriented , reliable , bytestream service. It also includes sophisticated rate- control enabling it to achieve high performance but also respond to changes in network capacity. UDP provides a datagram-oriented , unreliable service. (Datagrams are essentially individual packets.) It is lightweight. “Best effort” refers to a delivery service that simply makes a single attempt to deliver a CS 161, Spring 2010, Discussion 4 1 packet, but with no guarantees. The network-layer Internet protocol IP provides such a service, and be- cause UDP simply encapsulates its datagrams directly into IP packets with very little additional delivery properties, it too provides “best effort” service....
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This note was uploaded on 04/14/2010 for the course CS 161 taught by Professor Wagner during the Spring '10 term at University of Central Arkansas.

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02-16-2010-answers - CS 161 Computer Security Spring 2010...

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