1. CSE111: Great Ideas in Computer Science Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:50 645-4739 alphonce@buffalo.edu

2. cell phones off (please) 2

3. Announcements Exam 1 handback. HW3 due March 5. Second exam is March 17 (week after spring break). 3

4. Today’s Agenda Networking 4

5. What sorts of networks do we use? –Wired networks (in the labs) –Wireless (WIFI) networks (right now?) –Wireless cell phone networks –Wireless bluetooth (“personal area networks”) 5

6. Configurations Bus network –Devices connected to a common communications channel –Devices are peers –Ex. Typical wired network Star network –Devices connected to a central machine –Devices communicate only via central machine –Ex. Typical wifi network (access point) 6

7. Interconnecting networks Repeater –Propagate signals between networks Bridge –Propagate some signals between networks Switch –Bridge with multiple connections Router –Interface networks with different characteristics (e.g. ethernet bus to WiFi access point) 7

8. Routing messages Each device has an address on the network (IP address) Messages are routed based on destination IP address. –IPv4: 32 bit address (4.3 X 10 9 ) styx.cse.buffalo.edu (128.205.36.7) 10000000.11001101.00100100.00000111 –IPv6: 128 bit address (3.4 X 10 38 ) 8

9. Domain Name System (DNS) Translate from mnemonic form styx.cse.buffalo.edu to IP address 128.205.36.7 (dotted decimal notation) Determine DNS server –Windows run ‘ ifconfig /all ’ at cmd prompt –Mac Network preferences window Look at /etc/resolv.conf file 9

10. Reverse lookup: whois Try: whois 128.205.36.7 whois 142.103.7.7 10

11. 127.0.0.1 localhost, or “home” E.g. own machine provides service 11

12. Humor Image from: www.thinkgeek.com 12

13. 13 Humor Image from: www.thinkgeek.com

14. DNS hierarchy Root servers Caching domain servers Applications can cache as well 14

15. DNS attacks Denial-of-service –http://royal.pingdom.com/2009/01/26/dns-attack- slowed-down-hundreds-of-thousands-of-websites/http://royal.pingdom.com/2009/01/26/dns-attack- slowed-down-hundreds-of-thousands-of-websites/ DNS poisoning –You look my www.mybank.xyzwww.mybank.xyz –You go to web site of www.crooks.xyzwww.crooks.xyz –They put up page that looks like your bank’s page – and steal your banking log-on information. 15

16. Communication models Client-server –Print server –File server –Web server Peer-to-peer (P2P) –File sharing services –On-line gaming 16

17. Distributed Systems Banking system –ATM machines communicating with bank computers Automotive control system –Multiple interacting microprocessors –Self-contained network Google file system –Distributed data storage Facebook –Multiple users communicating/playing games Xbox Live –Many cooperating/competing players 17

18. Question from last class: Sometimes when I type a URL incorrectly, e.g. www.gogle.com or www.google.cm, I still get to the right place. How does this happen?www.gogle.com www.google.cm Answer from our technical staff: Great question! We can use nslookup to see that Google's IP address is 66.249.81.104. It's rational to assume that users will mistype the URL, so google has registered common misspellings in DNS. Thus gogle.com and gooogle.com both land you at 66.249.81.104, too. But google has to draw the line somewhere, or potentially anything could be a misspelling of google. So beyond those addresses, enterprising scam artists have purchases ggle.com (which is offered to you for sale) and goooogle.com (where, as the 10,000th visitor, you'll learn that it's your lucky day and that you qualify for special promotions). Google also owns google.net. I'm not sure about google.org. At first, I thought google missed the boat and some competitor was trying to camouflage itself to bootstrap off google's success, because google.org is clearly a different organization or project than google.com. But if you use the 'whois' utility[2], it looks like google.org was registered by the same organization that registered google.com. 18

19. VoIP Voice over IP “two processes on different machines transferring audio data via the P2P model” Issues: –Initiating/receiving calls –Interfacing with traditional telephone system –911 support 19

20. Internet Radio Unicast: one sender, one receiver N-Unicast: one sender, many receivers, each getting message from sender Multicast: one sender, many receivers; network routers help propagate single message from sender 20

21. 21 UNICAST SENDER RECEIVER

22. 22 N-UNICAST SENDER RECEIVERS

23. 23 MULTICAST SENDER RECEIVERS ROUTERS

24. HTML/XML Hyper Text Markup Language –Basic language for describing web pages –Not a general purpose programming language (we’ll explain why later) eXtensible Markup Language –XML is standard for designing mark-up languages –(X)HTML is conforms to XML 24

25. Attacks Virus –Infects software, reproduces itself –May do damage too Worm –Transfers itself through a network –May do damage too Trojan –Program designed to look legit, but which carries a nasty payload Spyware –“spies” on your activities (e.g. keystroke loggers) Phishing –Mentioned on Wednesday: a social engineering attack Denial of service –Mentioned on Wednesday: prevents legit users to access service 25

26. Protections Firewall –A filter for network traffic –Can block potentially dangerous traffic Proxy servers –Between client and real server –Isolates client-side of connection to not reveal structure Encryption –Unencrypted/encrypted traffic –Public/private keys 26