CSE111: Great Ideas in Computer Science Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:

cell phones off (please) 2

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

Today’s Agenda Networking 4

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

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

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

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 ( ) –IPv6: 128 bit address (3.4 X ) 8

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

Reverse lookup: whois Try: whois whois

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

Humor Image from: 12

13 Humor Image from:

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

DNS attacks Denial-of-service – slowed-down-hundreds-of-thousands-of-websites/ slowed-down-hundreds-of-thousands-of-websites/ DNS poisoning –You look my –You go to web site of –They put up page that looks like your bank’s page – and steal your banking log-on information. 15