1. CPS-356- Computer Networks Theo Benson (tbenson) https://www.cs.duke.edu/courses/spring15/comp sci356/ Based partly on lecture notes by Rodrigo Fonseca, David Mazières, Phil Levis, John Jannotti, Peterson & Davie

2. Cast Instructor: Theo Benson (tbenson) HTAs: Boyang Xu (boyangxu) UTA: Ang Li (li.ang) How to reach us: Piazza https://piazza.com/duke/spring2015/cps35601sp15/hom e

3. About Me

4. Overview Goal: learn concepts underlying networks –How do networks work? What can one do with them? –Gain a basic understanding of the Internet –Gain experience writing protocols –Tools to understand new protocols and applications “From 2 communicating machines to the entire Internet”

5. Prerequisites CPS-310 (Operating Systems). –We assume basic OS concepts (kernel/user, threads/processes, I/O, scheduling) Low-level programming or be willing to learn quickly –threads, locking, explicit memory management, … We allow C/C++ –You will be bit twiddling and byte packing…

6. Administrivia All assignments will be on the course page https://www.cs.duke.edu/courses/spring15/compsci356/ Text: Peterson and Davie, Computer Networks - A Systems Approach, 4 th or 5 th Editions You are responsible to check the web page! –All announcements will be there –Textbook chapters corresponding to lectures: read them before class –Handouts, due dates, programming resources, etc… –Subject to change (reload before checking assignments)

7. Grading “Written” component –Exams: Midterm (15%) and Final (25..%) –Homework: written assignments (10%) Short answer and design questions 4 Programming Projects (50%) – For group assignments, both students get the same grade for the assignment

8. Your work: important Assigned readings in the Syllabus Homework Labs (substantial, but worth your time). Most of them are ~500 lines of code, 20 hours of coding/debugging – Lab 1: SnowCast (basics on socket programming) – Lab 2: IP Project – Lab 3: reliable transport – Lab 4: congestion control (builds on Lab 3) Labs are distributed with skeleton code and most of them have reference implementations for testing Turn-ins include answers to pre-lab questions, source code, lab reports if we ask for them

9. Collaboration policy Discussion is encouraged Individual assignments must be completed independently Group assignments only need to turn in one copy of the files with group members noted in the submission Consult with course-website for full cheating policy – Any student caught cheating will be given a failing grade in the course

10. Late policy All homeworks are due at the beginning of the class on the due dates All labs/assignments are due at midnight EST The deadline for any assignment can be extended with a 10% penalty per day. – No deadline can be extended by more than two days. – Assignments will NOT be accepted 48 hours after the due date. Tight schedule Extension will delay next assignment – If you are ill: contact the instructor and provide a medical note.

11. Extra-Credit Extra-Credit is built into the course through several avenues: – Several assignments have an extra-credit component – There is an additional 5 th assignment that can be done for extra credit.

12. The first big question we study: How to design a global computer network

13. What’s a network? Wikipedia: A wide variety of systems of interconnected components are called networks. Examples of networks: what components are connected? – The Internet – Telephone networks – TV networks – Power networks – Sewage networks – Water networks – …. Why do we build networks? – To distribute/transfer something

14. Features of computer networks Generality Carry many different types of data Support an unlimited range of applications – Can you name several Internet applications?

15. Networks What is a network? –System of lines/channels that interconnect –E.g., railroad, highway, plumbing, postal, telephone, social, computer Computer Network –Moves information –Nodes: general-purpose computers (most nodes) –Links: wires, fiber optics, EM spectrum, composite…

16. Why are computer networks cooler? Many nodes are general-purpose computers Very easy to innovate and develop new uses of the network:you can program the nodes Contrast with the ossified Telephone network: –Can’t program most phones –Intelligence in the network, control by parties vested in the status quo, …

17. Growth of the Internet Source: Miguel Angel Todaro

18. Source: Cisco

19. Source: Facebook

20. What’s the Internet? The Internet is a large-scale general-purpose computer network. – Run more than one application The Internet transfers information between computers. The Internet is a network of networks.

21. What the Internet looks like email WWW phone... SMTP HTTP RTP... TCP UDP… IP ethernet PPP… CSMA async sonet... copper fiber radio... Ethernet ATM Framerelay IP/SONET Ethernet 802.X Wireless Host Tier 1 Tier 2 Tier 3 The Internet BGP RIP, OSFP Distance Vector Link-State Ethernet, CSMA/CD Bridges, Switches, Spanning Tree Bandwidth x Delay TCP Performance Modulation Coding FDMA, TDMA IP Blocks, CIDR, Subnets Longest Prefix Match, Fragmentation, MTU

22. Traceroute map of the Internet, ~5 million edges, circa 2003. opte.org

23. Why should you take this course? Impact –Social, economic, political, educational, … –Why would SOPA never work? –What does it mean to run out of IP addresses? –How could Egypt shut down the Internet internally? –How could Pakistan shut down Youtube globally? Continuously changing and evolving –Incredible complexity –Any fact you learn will be inevitably out of date –Learn general underlying principles Learn to program the network Networks are cool!

24. Questions?

25. Course outline The fundamentals – Reliable/secure communications over unreliable/insecure channels – Finding paths through the network – Resource sharing – Providing common services to applications Case studies on how to use the network Content distribution, DNS, p2p, social networks, search engines Socket programming

26. The networking field is broad and confusing…

27. A Plethora of Protocol Acronyms? BGP ARP HTTP DNS PPP OSPF DHCP TCP UDP SMTP FTP SSH MAC IP RIP NAT CIDR VLAN VTP NNTP POP IMAP RED ECN SACK SNMP TFTP TLS WAP SIP IPX STUN RTP RTSP RTCP PIM IGMP ICMP MPLS LDP HIP LISP LLDP BFD Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

28. A Heap of Header Formats? Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

29. TCP/IP Header Formats in Lego Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

30. A Big Bunch of Boxes? Router Switch Firewall NAT Load balancer DHCP server DNS server Bridge Hub Repeater Base station Proxy WAN accelerator Gateway Intrusion Detection System Packet shaper Route Reflector Label Switched Router Scrubber Packet sniffer Deep Packet Inspection Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

31. A Ton of Tools? traceroute nslookup ping ipconfig rancid whois tcpdump wireshark NDT iperf dummynet syslog trat snort bro arpwatch mrtg nmap ntop dig wget net-snmp Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

32. What Do Other People Say? “You networking people are very curious. You really love your artifacts.” “In my college networking class I fell asleep at the start of the semester when the IP header was on the screen, and woke up at the end of the semester with the TCP header on the screen.” “Networking is all details and no principles.” Is networking “just the (arti)facts”? Source: http://www.cs.princeton/~jrex/talks/conext-student10.ppt

33. Teaching/Learning about networking can be hard

34. I hope to make it easy for you Emphasis on fundamentals, concepts, and design skills – You’ll pay attention to details in labs Treat everything we learn as design examples – Why they are designed that way? – Is it a success or failure? – Will you do it the same way?

35. Roadmap Assignments: learn by implementing –Warm up: Snowcast, a networked music server Get a feel for how applications use the network Build knowledge from the ground up –Link individual nodes –Local networks with multiple nodes –IP: Connect hosts across several networks –Transport: Connect processes on different hosts –Applications A few cross-cutting issues –Security, multimedia, overlay networks, P2P…

36. Summary Course introduction – Administrivia – Course outline

37. Welcome back! Hope you had a great holiday break!

38. Coming Up Assignment 1 will be released on Monday. Next class: how do applications use the network? –Introduction to programming with Sockets –Peterson & Davie 1.4 –Beej’s Guide to Network Programming (link on the course website) Then… –We start moving up the network stack, starting from how two computers can talk to each other.