1. CS 3830 Day 6 Introduction 1-1

2. Announcements  Program 2 posted this afternoon (due date will be week of 9/24) Introduction 1-2

3. Introduction 1-3 The bad guys can use false source addresses  IP spoofing: send packet with false source address  Used in conjunction with DoS attacks  What if hacker not on the same subnet? A B C src:B dest:A payload

4. Introduction 1-4 The bad guys can record and playback  record-and-playback : sniff sensitive info (e.g., password), and use later (man-in-the-middle)  password holder is that user from system point of view A B C src:B dest:A user: B; password: foo src:C dest:A user: B; password: foo

5. Introduction 1-5 Network Security  more throughout this course  chapter 8: focus on security  cryptographic techniques: obvious uses and not so obvious uses

6. Introduction 1-6 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  end systems, access networks, links 1.3 Network core  circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History

7. Introduction 1-7 Internet History  1961: Kleinrock – queueing theory shows effectiveness of packet- switching  1964: Baran - packet- switching in military nets  1967: ARPAnet conceived by Advanced Research Projects Agency  1969: first ARPAnet node operational  Who had the first computer on the net?  1972:  ARPAnet public demonstration  NCP (Network Control Program) first host-host protocol  first e-mail program  ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

8. Introduction 1-8 Internet History  1970: ALOHAnet satellite network in Hawaii  1974: Cerf and Kahn - architecture for interconnecting networks  1976: Ethernet at Xerox PARC  late70’s: proprietary architectures: DECnet, SNA, XNA  late 70’s: switching fixed length packets (ATM precursor)  1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:  minimalism, autonomy - no internal changes required to interconnect networks  best effort service model  stateless routers  decentralized control define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets

9. Introduction 1-9 Internet History  1983: deployment of TCP/IP  1982: smtp e-mail protocol defined  1983: DNS defined for name-to-IP- address translation  1985: ftp protocol defined  1988: TCP congestion control  new national networks: Csnet, BITnet, NSFnet, Minitel  100,000 hosts connected to confederation of networks 1980-1990: new protocols, a proliferation of networks

10. Introduction 1-10 Internet History  Early 1990’s: ARPAnet decommissioned  1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)  early 1990s: Web  HTML, HTTP: Berners-Lee  1994: Mosaic, later Netscape  late 1990’s: commercialization of the Web Late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing  network security to forefront  est. 50 million+ hosts  backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps

11. Introduction 1-11 Internet History 2007:  ~500 million hosts  Voice, Video over IP  P2P applications: BitTorrent, Skype, etc.  more applications: YouTube, gaming  wireless, mobility Current: ??  Do some research and find some interesting statistics

12. Introduction 1-12 Introduction: Summary Covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  Internet structure  performance: loss, delay, throughput  layering, service models  security  history You now have:  context, overview, “feel” of networking  more depth, detail to follow!

13. 2: Application Layer 13 Chapter 2: Application layer  2.1 Principles of network applications  2.2 Web and HTTP  2.3 FTP  2.4 Electronic Mail  SMTP, POP3, IMAP  2.5 DNS  2.6 P2P applications  2.7 Socket programming with TCP  2.8 Socket programming with UDP

14. 2: Application Layer 14 Chapter 2: Application Layer Our goals:  conceptual, implementation aspects of network application protocols:  transport-layer service models  client-server paradigm  peer-to-peer paradigm  learn about protocols by examining popular application-level protocols:  HTTP  FTP  SMTP / POP3 / IMAP  DNS  programming network applications  socket API (Java)

15. 2: Application Layer 15 Chapter 2: Application layer  2.1 Principles of network applications  2.2 Web and HTTP  2.3 FTP  2.4 Electronic Mail  SMTP, POP3, IMAP  2.5 DNS  2.6 P2P applications  2.7 Socket programming with TCP  2.8 Socket programming with UDP  2.9 Building a Web server

16. 2: Application Layer 16 Application architectures  Client-server  Peer-to-peer (P2P)  Hybrid of client-server and P2P

17. 2: Application Layer 17 Client-server architecture server:  always-on host  permanent IP address  server farms for scaling clients:  communicate with server  may be intermittently connected  may have dynamic IP addresses  do not communicate directly with each other client/server

18. 2: Application Layer 18 Pure P2P architecture  no always-on server  arbitrary end systems directly communicate  peers are intermittently connected and change IP addresses Highly scalable but difficult to manage peer-peer

19. 2: Application Layer 19 Hybrid of client-server and P2P Skype  voice-over-IP P2P application  centralized server: finding address of remote party:  client-client connection: direct (not through server) Instant messaging  chatting between two users is P2P  centralized service: client presence detection/location user registers its IP address with central server when it comes online user contacts central server to find IP addresses of buddies

20. 2: Application Layer 20 Processes communicating Process: program running within a host.  within same host, two processes communicate using inter-process communication (defined by OS).  processes in different hosts communicate by exchanging messages Client process: process that initiates communication Server process: process that waits to be contacted r Note: applications with P2P architectures have client processes & server processes