Net working � So f ar we have t alked pr imar ily about OS 15: Net working Basics support f or individual comput er syst ems � Today we are going t o t alk about net working comput er syst ems t oget her Last Modif ied: 7/ 3/ 2004 1:47:08 PM -1 -2 A Net work Quest ions � A net work is simply a collect ion of nodes, � What will be t he f or mat of dat a exchanged? How do we agr ee on a language among all kinds of connect ed by links, t hat communicat e and nodes? cooperat e � Tr ansmission acr oss links is f ault y can � Nodes = End Host s (PCs, PDAs, t oast er s?), cor r upt / lose dat a. How can we r eliably exchange I nt er nal Nodes (Rout er s, swit ches, hubs,..) inf or mat ion? � Links = Et her net , Wir eless, point t o point ,… � How do we f ind t he r ight pat h bet ween t wo nodes? I f t her e ar e many how do we choose t he best one? � How do nodes r ef er t o one anot her or addr ess one anot her? � What is t he oper at ing syst ems r ole in all t his? -3 -4 Communicat ion? P rot ocol � I f t wo ent it ies are going t o communicat e, � Def ines t he f ormat and t he order of t hey must agree on t he expect ed order and messages exchanged bet ween meaning of messages t hey exchange. communicat ing ent it ies � Asking f or t he t ime prot ocol � Def ines t he act ions expect ed t o be t aken on t he receipt or t he t ransmission of a � SUCCESSFUL PROTOCOL EXCHANGE message • Hi … Hi… Got t he t ime?… .t wo oclock � ABORTED PROTOCOL • Hi… Don’t bot her meXX � PROTOCOL MI SMATCH • Allo… Hello..Quelle heuere a’t il … ..XX< blank st are> -5 -6 1
Net working prot ocols Layered Archit ect ures � Ok let s def ine t he “language” f or all � Br eak-up design problem int o smaller, more int eract ions over t he net work?? manageable problems � One single language t hat can suppor t ever yt hing � Layers f rom web browsing t o email t o f t p t o � Design prot ocols t o support each well dist ribut ed f ile syst ems? def ined t ask � Human beings are able t o handle lot s of complexit y in t heir prot ocol processing. � Not one language f or ever yt hing!! � Ambiguously def ined pr ot ocols � Many pr ot ocols all at once � How do comput ers manage complex prot ocol processing? -7 -8 I nt ernet prot ocol st ack P rot ocol st ack Language Spoken users Among Peer s network user X English user Y HTTP, SMTP, FTP, TELNET, DNS, … Application e-mail client SMTP e-mail server TCP, UDP. Transport TCP TCP server TCP server IP IP Network IP server IP server ethernet IEEE 802.3 standard ethernet Point-to-point links, Physical driver/card driver/card LANs, radios, ... electric signals -9 -10 P acket Swit ching P rot ocol encapsulat ion SMTP Commands TCP Headers I P Headers � Packet s indicat e t heir dest inat ion user X user Y “Hello” Et hernet Frame � No predet ermined pat h f or a packet t o e-mail client e-mail server t ake “Hello” � Each int ermediat e not e rout es t he packet “Hello” closer t o it s dest inat ion TCP layer TCP layer IP layer “Hello” IP layer ethernet ethernet “Hello” driver/card driver/card -11 -12 2
P rot ocol st ack: A small I nt ernet packet f orwarding W Host A Host B b,e4 w,e5 Router R Router W B Scenario: HTTP HTTP A wants to send data V to B. TCP TCP R r3 IP IP IP IP r2,e2 r1,e1 ethernet link link ethernet ethernet ethernet a,e3 A -13 -14 Tracerout e/ t racert assenger Forwarding ☺ P Boise Airport Syracuse Airport Tickets Tickets Newark Chicago Baggage Baggage Gates Gates Gates Gates Runway Runway runway runway Runway Runway -15 -16 Graphical Tracerout e (plus I nt ernet Map DNS inf ormat ion ☺ ) � Tracerout e gives one slice t hrough t he I nt ernet t opology � What does t he I nt ernet really look like? � That is a act ually a har d quest ion t o answer � I nt er net At las Pr oj ect • ht t p:/ / www.caida.org/ proj ect s/ int ernet at las/ • Techniques, sof t ware, and prot ocols f or mapping t he I nt ernet , f ocusing on I nt ernet t opology, perf ormance, workload, and rout ing dat a -17 -18 3
CAI DA: NSFNET growt h unt il The I nt ernet around 1990 1995 Backbone nodes elevat ed Low Tr af f ic Volume High -19 -20 NSF Net working Archit ect ure Net work Access P oint of Lat e 1990s � NSFNET Backbone Proj ect successf ully � Allows I nt ernet Service Providers (I SPs), t ransit ioned t o a new net working government , research, and educat ional archit ect ure in 1995. organizat ions t o int erconnect and exchange inf or mat ion � vBNS ( ver y high speed Backbone Net wor k Ser vices) - NSF f unded, provided by MCI � I SP s connect t heir net works t o t he NAP � 4 or iginal Net wor k Access Point s (NSF f or t he purpose of exchanging t raf f ic wit h awar ded) ot her I SPs � NSF f unded Rout ing Ar bit er pr oj ect � Such exchange of I nt ernet t raf f ic is of t en � Net wor k Ser vice Pr ovider s (not NSF f unded) ref erred t o as "peering" -21 -22 Locat ion (longit ude) CAI DA’s skit t er plot The I nt ernet in 1997 Top 15 ASes ar e in Nor t h Amer ica (14 in US, 1 in Canada) Highly connect ed Many links US t o Asia and Eur ope; f ew dir ect Asia/ Eur ope Links Asia Few connect ions Eur ope Skit t er dat a 16 monit or s pr obing appr oximat ely 400,000 dest inat ions 626,773 I P addr esses 1,007.723 I P links 48,302 (52%) of globally r out able net work pref ixes Nort h America -23 -24 4
Names and addresses: DNS: Domain Name Syst em why bot h? People: many ident if iers: Domain Name Syst em: � Name: www.google.com � SSN, name, P assport # � dist ribut ed dat abase � I P addr ess (one of t hem): 216.239.39.147 implement ed in hierarchy of I nt ernet host s, rout ers: many name servers � (Also Et hernet or ot her link- layer addresses.) � I P addr ess (32 bit ) - � applicat ion- layer prot ocol � I P addr esses ar e f ixed- size number s. used f or addressing host , rout ers, name servers t o dat agrams � 32 bit s. 216.239.39.147 = communicat e t o resolve names � “name”, e.g., 101011000.11101111.00100111.10010011 (address/ name t ranslat ion) gaia.cs.umass.edu - used � Names are memor izable, f lexible: � not e: core I nt ernet by humans f unct ion implement ed as � Variable- lengt h Q: map bet ween I P applicat ion- layer prot ocol � Many names f or a single I P address. addr esses and name ? � complexit y at net work’s � Change address doesn’t imply change name. “edge” � iPv6 addresses are 128 bit – even harder t o memorize! -25 -26 How t o get names and Mapping Not 1 t o 1 numbers? � One name may map t o more t han one I P � Acquisit ion of Names and numbers are bot h address regulat ed � I P addr esses ar e per net wor k int er f ace � Why? � Mult i -homed machines have mor e t han one net wor k int er f ace - each wit h it s own I P address � Example: r out er s must be like t his � One I P address may map t o more t han one name � One server machine may be t he web server (www.f oo,com), mail server (mail.f oo.com)et c. -27 -28 How t o get a name? Domain name st ruct ure � First , get a domain name t hen you are f ree t o assign sub names in t hat domain root (unnamed) � How t o get a domain name coming up ... ... com edu gov mil net org fr gr us uk � Bef or e you ask f or a domain name t hough ccTLDs gTLDs � Should under st and domain name st r uct ur e… � Know t hat you ar e r esponsible f or pr oviding google clarkson ustreas second level (sub-)domains aut hor it at ive DNS ser ver (act ually a pr imar y and one or mor e secondar y DNS ser ver s) f or t hat domain and r egist r at ion inf or mat ion gTLDs= Generic Top Level Domains t hr ough “whois” ccTLDs = Country Code Top Level Domains -29 -30 5
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