,! ,hit*hik]s ,guide to ! ,int]net #be ,augu/ #aihg ,ed ,krol kroluxc4cso4uiuc4edu ,?is docum5t 0 produc$ ?r\gh fund+ ( ! ,national ,sci5ce ,f\ndation4 ,copyright 7,c7 #aihg1 by ! ,bo>d ( ,tru/ees ( ,! ,univ]sity ( ,ill9ois4 ,p]mission to duplicate ?is docum5t1 9 :ole or "p1 is grant$ provid$ ref]5ce is made to ! s\rce & ?is copyright is includ$ 9 :ole copies4 ,?is docum5t assumes t "o is famili> ) ! work+s ( a non-connect$ simple ,,ip network 7e4g4 a few #d4b ,,bsd sy/ems on an ,e!rnet n connect$ to any:]e else74 ,app5dix ,a conta9s rem$ial in=mation to get "o to ?is po9t4 ,its purpose is to get t p]son1 famili> ) a simple net1 v]s$ 9 ! oral tradition ( ! ,int]net to ! po9t t t net c be connect$ to ! ,int]net ) little dang] to ei!r4 ,x is n a tutorial1 x consi/s ( po9t]s to o!r places1 lit]ature1 & h9ts :i* are n normally docum5t$4 ,s9ce ! ,int]net is a dynamic environm5t1 *anges to ?is docum5t w be made regul>ly4 ,! au?or welcomes comm5ts & sugge/ions4 ,?is is especially true ( t]ms = ! gloss>y 7def9itions are n necess>y74 ,9 ! beg9n+ !re 0 ! ,a,r,p,anet1 a wide area exp]im5tal network connect+ ho/s & t]m9al s]v]s toge!r4 ,proc$ures 7 set up to regulate ! allocation ( addresses & to create volunt>y /&>ds = ! network4 ,z local area networks became m p]vasive1 _m ho/s became gateways to local networks4 ,a network lay] to all[ ! int]op]ation ( ^! networks 0 develop$ & call$ ,,ip 7,int]net ,protocol74 ,ov] "t o!r gr\ps creat$ long haul ,,ip bas$ networks 7,,nasa1 ,,nsf1 /ates44474 ,^! nets1 too1 int]op]ate because ( ,,ip4 ,! collection ( all ( ^! int]op]at+ networks is ! ,int]net4 ,two gr\ps d mu* ( ! rese>* & in=mation "w ( ! ,int]net 7,,isi & ,,sri74 ,,isi 7! ,in=mational ,sci5ces ,in/itute7 does mu* ( ! rese>*1 /&>dization1 & allocation "w ( ! ,int]net4 ,,sri ,int]national provides in=mation s]vices = ! ,int]net4 ,9 fact1 aft] y are connect$ to ! ,int]net mo/ ( ! in=mation 9 ?is docum5t c be retriev$ f ! ,network ,in=mation ,c5t] 7,,nic7 run by ,,sri4 ,op]at+ ! ,int]net ,ea* network1 be x ! ,a,r,p,anet1 ,n,s,fnet or a regional network1 has its own op]ations c5t]4 ,! ,a,r,p,anet is run by ,,bbn1 ,inc4 "u contract f ,,d>pa4 ,_! facility is call$ ! ,network ,op]ations ,c5t] or ,,noc4 ,cornell ,univ]sity tempor>ily op]ates ,n,s,fnet 7call$ ! ,network ,in=mation ,s]vice ,c5t]1 ,,nisc74 ,x goes on to ! -#b- regionals hav+ simil> facilities to monitor & keep wat* ov] ! go+s on ( _! portion ( ! ,int]net4 ,9 addition1 !y all %\ld h "s k ( :at is happ5+ to ! ,int]net 9 total4 ,if a problem comes up1 x is sugge/$ t a campus network liaison %\ld contact ! network op]ator to :i* he is directly connect$4 ,t is1 if y are connect$ to a regional network 7:i* is gateway$ to ! ,n,s,fnet1 :i* is connect$ to ! ,a,r,p,anet4447 & h a problem1 y %\ld contact y\r regional network op]ations c5t]4 ,r,f,cs ,! int]nal work+s ( ! ,int]net are def9$ by a set ( docum5ts call$ ,r,f,cs 7,reque/ = ,comm5ts74 ,! g5]al process = creat+ an ,,rfc is = someone want+ some?+ =maliz$ to write a docum5t describ+ ! issue & mail+ x to ,jon ,po/el 7po/elisi4edu74 ,he acts z a ref]ee = ! proposal4 ,x is !n comm5t$ ^u by all ^? wi%+ to take "p 9 ! discussion 7electronically ( c\rse74 ,x may g ?r\gh multiple revisions4 ,%\ld x be g5]ally accept$ z a good idea1 x w be assign$ a numb] & fil$ ) ! ,r,f,cs4 ,! ,r,f,cs c be divid$ into five gr\ps3 requir$1 sugge/$1 directional1 in=mational & obsolete4 ,requir$ ,,rfc's 7e4g4 ,,rfc-#gia1 ,! ,int]net ,protocol7 mu/ be implem5t$ on any ho/ connect$ to ! ,int]net4 ,sugge/$ ,r,f,cs are g5]ally implem5t$ by network ho/s4 ,lack ( !m does n preclude access to ! ,int]net1 b may impact its usability4 ,,rfc-#gic 7,transmission ,control ,protocol7 is a sugge/$ ,,rfc4 ,directional ,r,f,cs 7 discuss$ & agre$ to1 b _! application has nev] come into wide use4 ,?is may be due to ! lack ( wide ne$ = ! specific application 7,,rfc-#icg ,! ,po/ ,(fice ,protocol7 or t1 al?\gh te*nically sup]ior1 ran aga9/ o!r p]vasive approa*es 7,,rfc-#hia ,hello74 ,x is sugge/$ t %\ld ! facility be requir$ by a p>ticul> site1 animplem5tation be done 9 accordance ) ! ,,rfc4 ,?is insures t1 %\ld ! idea be "o ^: "t has come1 ! implem5tation w be 9 accordance ) "s /&>d & w be g5]ally usable4 ,in=mational ,r,f,cs conta9 factual in=mation ab\t ! ,int]net & its op]ation 7,,rfc-#iij1 ,assign$ ,numb]s74 ,f9ally1 z ! ,int]net & te*nology h gr[n1 "s ,r,f,cs h become unnecess>y4 ,^! obsolete ,r,f,cs _c be ignor$1 h[ev]4 ,frequ5tly :5 a *ange is made to "s ,,rfc t causes a new "o to be issu$ obsolet+ o!rs1 ! new ,,rfc only conta9s explanations & motivations = ! *ange4 ,und]/&+ ! model on :i* ! :ole facility is bas$ may involve read+ ! orig9al & subsequ5t ,r,f,cs on ! topic4 -#c- 7,app5dix ,b conta9s a li/ ( :at are consid]$ to be ! major ,r,f,cs necess>y = und]/&+ ! ,int]net74 ,! ,network ,in=mation ,c5t] ,! ,,nic is a facility available to all ,int]net us]s :i* provides in=mation to ! community4 ,!re are ?ree means ( ,,nic contact3 network1 telephone1 & mail4 ,! network accesses are ! mo/ preval5t4 ,int]active access is frequ5tly us$ to d qu]ies ( ,,nic s]vice ov]views1 look up us] & ho/ names1 & scan li/s ( ,,nic docum5ts4 ,x is available by us+ telnet sri-nic4arpa on a ,,bsd sy/em & foll[+ ! directions provid$ by a us] fri5dly prompt]4 ,f pok+ ar\nd 9 ! databases provid$ "o might decide t a docum5t nam$ ,,net9fo3,,nug4,,doc 7,! ,us]s ,guide to ! ,a,r,p,anet7 w\ld be wor? hav+4 ,x c\ld be retriev$ via an anonym\s ,,ftp4 ,an anonym\s ,,ftp w\ld proce$ some?+ l ! foll[+4 7,! dialogue may v>y slightly dep5d+ on ! implem5tation ( ,,ftp y are us+74 ftp sri-nic4arpa ,connect$ to sri-nic4arpa4 #bbj ,,sri,,nic4,,arpa ,,ftp ,s]v] ,process #e,z7#dg7-f at ,w$ #ag-;,jun-#hg #ab3jj ,,pdt ,"n 7sri-nic4arpa3myname73 anonym\s #cca ,,anonym\s us] ok1 s5d real id5t z password4 ,password3 myname #bcj ,us] ,,anonym\s logg$ 9 at ,w$ #ag-;,jun-#hg #ab3ja ,,pdt1 job #ae4 ftp get net9fo3nug4doc #bjj ,port #ah4add at ho/ #abh4agd4e4ej accept$4 #aej ,,ascii retrieve ( ,,net9fo,,nug4,,doc4#aa />t$4 #bbf ,transf] ,complet$ #aegfge 7#h7 bytes transf]r$ local3 net9fo3nug4doc remote3net9fo3nug4doc #aegfge bytes 9 #d4e;e#jb seconds 7#j4cd ,kbytes_/s7 ftp quit #bba ,,quit comm& receiv$4 ,goodbye4 7,ano!r good initial docum5t to fet* is ,,net9fo3,,:at-,,!-,,nic-,,does4,,txt76 ,que/ions ( ! ,,nic or problems ) s]vices c be ask$ ( or report$ to us+ electronic mail4 ,! foll[+ addresses c be us$3 ,,nic,,sri-,,nic4,,arpa ,g5]al us] assi/ance1 docum5t reque/s ,,regi/r>,,sri-,,nic4,,arpa ,us] regi/ration & ,,:ois updates ,,ho/ma/],,sri-,,nic4,,arpa ,ho/name & doma9 *anges & updates ,,action,,sri-,,nic4,,arpa ,,sri-,,nic comput] op]ations ,,sugge/ions,,sri-,,nic4,,arpa ,comm5ts on ,,nic publications & s]vices -#d- ,= p )\t network access1 or if ! numb] ( docum5ts is l>ge1 _m ( ! ,,nic docum5ts are available 9 pr9t$ =m = a small *>ge4 ,"o frequ5tly ord]$ docum5t = />t+ sites is a comp5dium ( major ,r,f,cs4 ,telephone access is us$ prim>ily = que/ions or problems ) network access4 7,see app5dix ,b = mail_/telephone contact numb]s74 ,! ,n,s,fnet ,network ,s]vice ,c5t] ,! ,n,s,fnet ,network ,s]vice ,c5t] 7,,nnsc7 is fund$ by ,,nsf to provide a fir/ level ( aid to us]s ( ,n,s,fnet %\ld !y h que/ions or enc\nt] problems trav]s+ ! network4 ,x is run by ,,bbn ,inc4 ,k>5 ,r\bicek 7r\biceknnsc4nsf4net7 is ! ,,nnsc us] liaison4 ,! ,,nnsc1 :i* curr5tly has in=mation & docum5ts onl9e & 9 pr9t$ =m1 plans to di/ribute news ?r\gh network mail+ li/s1 bullet9s1 newslett]s1 & onl9e reports4 ,! ,,nnsc also ma9ta9s a database ( contact po9ts & s\rces ( additional in=mation ab\t ,n,s,fnet compon5t networks & sup]comput] c5t]s4 ,prospective or curr5t us]s :o d n "k :om to call conc]n+ que/ions ab\t ,n,s,fnet use1 %\ld contact ! ,,nnsc4 ,! ,,nnsc w answ] g5]al que/ions1 &1 = detail$ in=mation relat+ to specific compon5ts ( ! ,int]net1 w help us]s f9d ! appropriate contact = fur!r assi/ance4 7,app5dix ,b7 ,mail ,reflectors ,! way mo/ p keep up to date on network news is ?r\gh subscription to a numb] ( mail reflectors4 ,mail reflectors are special electronic mailboxes :i*1 :5 !y receive a message1 res5d x to a li/ ( o!r mailboxes4 ,?is 9 effect creates a discussion gr\p on a p>ticul> topic4 ,ea* subscrib] sees all ! mail =w>d$ by ! reflector1 & if "o wants to put 8 two c5ts 9 s5ds a message ) ! comm5ts to ! reflector4444 ,! g5]al =mat to subscribe to a mail li/ is to f9d ! address reflector & app5d ! /r+ -,,reque/ to ! mailbox "n 7n ! ho/ "n74 ,= example1 if y want$ to take "p 9 ! mail+ li/ = ,n,s,fnet reflect$ by ,,nsfnet,,nnsc4,,nsf4,,net1 "o s5ds a reque/ to -#e- ,,nsfnet-,,reque/,,nnsc4,,nsf4,,net4 ,?is may be a wond]ful s*eme1 b ! problem is t y mu/ "k ! li/ exi/s 9 ! fir/ place4 ,x is sugge/$ t1 if y are int]e/$1 y read ! mail f "o li/ 7l ,,nsfnet7 & y w probably become famili> ) ! exi/5ce ( o!rs4 ,a regi/ration s]vice = mail reflectors is provid$ by ! ,,nic 9 ! files ,,net9fo3,,int]e/-,,gr\ps-#a4,,txt1 ,,net9fo3,,int]e/-,,gr\ps-#b4,,txt1 & ,,net9fo3,,int]e/-,,gr\ps- #c4,,txt4 ,! ,,nsfnet mail reflector is t>get$ at ^? p :o h a day to day int]e/ 9 ! news ( ! ,n,s,fnet 7! backbone1 regional network1 & ,int]net int]-connection site work]s74 ,! messages are reflect$ by a c5tral location & are s5t z sep>ate messages to ea* subscrib]4 ,?is creates hundr$s ( messages on ! wide area networks :]e b&wid? is ! sc>ce/4 ,!re are two ways 9 :i* a campus c\ld spread ! news & n cause ^! messages to inundate ! wide area networks4 ,"o is to re-reflect ! message on ! campus4 ,t is1 set up a reflector on a local ma*9e :i* =w>ds ! message to a campus di/ribution li/4 ,! o!r is to create an alias on a campus ma*9e :i* places ! messages into a notesfile on ! topic4 ,campus us]s :o want ! in=mation c\ld access ! notesfile & see ! messages t h be5 s5t s9ce _! la/ access4 ,"o might also elect to h ! campus wide area network liaison scre5 ! messages 9 ei!r case & only =w>d ^? :i* are consid]$ ( m]it4 ,ei!r ( ^! s*emes all[s "o message to be s5t to ! campus1 :ile all[+ wide di/ribution )94 ,address ,allocation ,be=e a local network c be connect$ to ! ,int]net x mu/ be allocat$ a unique ,,ip address4 ,^! addresses are allocat$ by ,,isi4 ,! allocation process consi/s ( gett+ an application =m receiv$ f ,,isi4 7,s5d a message to ho/ma/]sri-nic4arpa & ask = ! template = a connect$ address74 ,?is template is fill$ out & mail$ back to ho/ma/]4 ,an address is allocat$ & e-mail$ back to y4 ,?is c also be done by po/al mail 7,app5dix ,b74 ,,ip addresses are #cb bits long4 ,x is usually writt5 z f\r decimal numb]s sep>at$ by p]iods 7e4g41 #aib4ag4e4ajj74 ,ea* numb] is ! value ( an octet ( ! #cb bits4 ,x 0 se5 f ! beg9n+ t "s networks might *oose to organize !mselves z v flat 7"o net ) a lot ( nodes7 & "s might organize hi]>*ically -#f- 7_m int]connect$ nets ) few] nodes ea* & a backbone74 ,to provide = ^! cases1 addresses 7 diff]5tiat$ into class ,a1 ,b1 & ,c networks4 ,?is classification _h to ) ! int]pretation ( ! octets4 ,class ,a networks h ! fir/ octet z a network address & ! rema9+ ?ree z a ho/ address on t network4 ,class ,c addresses h ?ree octets ( network address & "o ( ho/4 ,class ,b is split two & two4 ,!re=e1 !re is an address space = a few l>ge nets1 a reasonable numb] ( m$ium nets & a l>ge numb] ( small nets4 ,! top two bits 9 ! fir/ octet are cod$ to tell ! address =mat4 ,all ( ! class ,a nets h be5 allocat$4 ,s "o has to *oose betwe5 ,class ,b & ,class ,c :5 plac+ an ord]4 7,!re are also class ,d 7,multica/7 & ,e 7,exp]im5tal7 =mats4 ,multica/ addresses w likely come into great] use 9 ! ne> future1 b are n frequ5tly us$ n[74 ,9 ! pa/ sites requir+ multiple network addresses reque/$ multiple discrete addresses 7usually ,class ,c74 ,?is 0 done because mu* ( ! s(tw>e available 7n ably #d4b;,,bsd7 c\ld n deal ) subnett$ addresses4 ,in=mation on h[ to rea* a p>ticul> network 7r\t+ in=mation7 mu/ be /or$ 9 ,int]net gateways & packet swit*es4 ,"s ( ^! nodes h a limit$ capability to /ore & ex*ange r\t+ in=mation 7limit$ to ab\t #cjj networks74 ,!re=e1 x is sugge/$ t any campus ann\nce 7make kn[n to ! ,int]net7 no m ?an two discrete network numb]s4 ,if a campus expects to be con/ra9$ by ?is1 x %\ld consid] subnett+4 ,subnett+ 7,,rfc-#icb7 all[s "o to ann\nce "o address to ! ,int]net & use a set ( addresses on ! campus4 ,basically1 "o def9es a mask :i* all[s ! network to diff]5tiate betwe5 ! network portion & ho/ portion ( ! address4 ,by us+ a diff]5t mask on ! ,int]net & ! campus1 ! address c be int]pret$ 9 multiple ways4 ,= example1 if a campus requires two networks int]nally & has ! #cb1jjj addresses beg9n+ #abh4agd4,x4,x 7a ,class ,b address7 allocat$ to x1 ! campus c\ld allocate #abh4agd4e4,x to "o "p ( campus & #abh4agd4aj4,x to ano!r4 ,by adv]tis+ #abh4agd to ! ,int]net ) a subnet mask ( ,,ff4,,ff4#jj4jj1 ! ,int]net w\ld treat ^! two addresses z "o4 ,)9 ! campus a mask ( ,,ff4,,ff4,,ff4#jj w\ld be us$1 all[+ ! campus to treat ! addresses z sep>ate entities4 7,9 reality y don't pass ! subnet mask ( ,,ff4,,ff4#jj4jj to ! ,int]net1 ! octet mean+ is implicit 9 its be+ a class ,b address74 ,a ^w ( w>n+ is necess>y4 ,n all sy/ems "k h[ to d subnett+4 ,"s #d4b;,,bsd sy/ems require additional s(tw>e4 #d4c;,,bsd sy/ems subnet z releas$4 ,o!r devices -#g- & op]at+ sy/ems v>y 9 ! problems !y h deal+ ) subnets4 ,frequ5tly ^! ma*9es c be us$ z a leaf on a network b n z a gateway )9 ! subnett$ portion ( ! network4 ,z "t passes & m sy/ems become #d4c;,,bsd bas$1 ^! problems %\ld disappe>4 ,!re has be5 "s confusion 9 ! pa/ ov] ! =mat ( an ,,ip broadca/ address4 ,"s ma*9es us$ an address ( all z]os to mean broadca/ & "s all ones4 ,?is 0 confus+ :5 ma*9es ( bo? type 7 connect$ to ! same network4 ,! broadca/ address ( all ones has be5 adopt$ to end ! grief4 ,"s sy/ems 7e4g4 #d4b ,,bsd7 all[ "o to *oose ! =mat ( ! broadca/ address4 ,if a sy/em does all[ ?is *oice1 c>e %\ld be tak5 t ! all ones =mat is *os54 7,?is is expla9$ 9 ,,rfc-#ajji & ,,rfc-#ajaj74 ,int]net ,problems ,!re are a numb] ( problems ) ! ,int]net4 ,solutions to ! problems range f s(tw>e *anges to long t]m rese>* projects4 ,"s ( ! major ones are detail$ bel[3 ,numb] ( ,networks ,:5 ! ,int]net 0 design$ x 0 to h ab\t #ej connect$ networks4 ,) ! explosion ( network+1 ! numb] is n[ approa*+ #cjj4 ,! s(tw>e 9 a gr\p ( critical gateways 7call$ ! core gateways ( ! ,a,r,p,anet7 are n able to pass or /ore mu* m ?an t numb]4 ,9 ! %ort t]m1 core reallocation & recod+ has rais$ ! numb] slightly4 ,by ! summ] ( '#hh ! curr5t ,,pdp-#aa core gateways w be replac$ ) ,,bbn ,butt]fly gateways :i* w solve ! problem4 ,r\t+ ,issues ,along ) %e] mass ( ! data necess>y to r\te packets to a l>ge numb] ( networks1 !re are _m problems ) ! updat+1 /ability1 & optimality ( ! r\t+ algori?ms4 ,mu* rese>* is be+ done 9 ! area1 b ! optimal solution to ^! r\t+ problems is /ill ye>s away4 ,9 mo/ cases ! ! r\t+ we h today works1 b sub-optimally & sometimes unpr$ictably4 -#h- ,tru/ ,issues ,gateways ex*ange network r\t+ in=mation4 ,curr5tly1 mo/ gateways accept on fai? t ! in=mation provid$ ab\t ! /ate ( ! network is correct4 ,9 ! pa/ ?is 0 n a big problem s9ce mo/ ( ! gateways belong$ to a s+le adm9i/rative entity 7,,d>pa74 ,n[ ) multiple wide area networks "u diff]5t adm9i/rations1 a rogue gateway some:]e 9 ! net c\ld cripple ! ,int]net4 ,!re is design "w go+ on to solve bo? ! problem ( a gateway do+ unreasonable ?+s & provid+ en\gh in=mation to reasonably r\te data betwe5 multiply connect$ networks 7multi-hom$ networks74 ,capacity ,conge/ion ,_m portions ( ! ,a,r,p,anet are v conge/$ dur+ ! busy "p ( ! day4 ,additional l9ks are plann$ to alleviate ?is conge/ion1 b ! implem5tation w take a few mon?s4 ,^! problems & ! future direction ( ! ,int]net are det]m9$ by ! ,int]net ,ar*itect 7,dave ,cl>k ( ,,mit7 be+ advis$ by ! ,int]net ,activities ,bo>d 7,,iab74 ,?is bo>d is compos$ ( *airm5 ( a numb] ( committees ) responsibility = v>i\s specializ$ areas ( ! ,int]net4 ,! committees compos+ ! ,,iab & _! *airm5 are3 ,committee ,*air ,autonom\s ,networks ,deborah ,e/r9 ,end-to-,end ,s]vices ,bob ,brad5 ,int]net ,ar*itecture ,dave ,mills ,int]net ,eng9e]+ ,phil ,gross ,,egp#b ,mike ,petry ,"n ,doma9 ,plann+ ,d\g ,k+/on ,gateway ,monitor+ ,craig ,p>tridge ,int]nic ,jake ,fe9l] ,p]=mance ,conge/ion ,control,robert ,/9e ,,nsf ,r\t+ ,*uck ,h$rick ,misc4 ,mil,sup ,issues ,mike ,/4 ,johns ,privacy ,/eve ,k5t ,,ir9et ,requirem5ts ,v9t ,c]f ,robu/ness ,survivability ,jim ,ma?is ,sci5tific ,requirem5ts ,b>ry ,le9] ,note t "u ,int]net ,eng9e]+1 !re are a set ( task =ces & *airs to look at %ort t]m conc]ns4 ,! *airs ( ^! task =ces are n "p ( ! ,,iab4 -#i- ,r\t+ ,r\t+ is ! algori?m by :i* a network directs a packet f its s\rce to its de/9ation4 ,to appreciate ! problem1 wat* a small *ild try+ to f9d a table 9 a re/aurant4 ,f ! adult po9t ( view ! /ructure ( ! d9+ room is se5 & an optimal r\te easily *os54 ,! *ild1 h[ev]1 is pres5t$ ) a set ( pa?s betwe5 tables :]e a good pa?1 let alone ! optimal "o to ! goal is n disc]nible4999999 ,a little m backgr\nd might be appropriate4 ,,ip gateways 7m correctly r\t]s7 are boxes :i* h connections to multiple networks & pass traffic betwe5 ^! nets4 ,!y decide h[ ! packet is to be s5t bas$ on ! in=mation 9 ! ,,ip head] ( ! packet & ! /ate ( ! network4 ,ea* int]face on a r\t] has an unique address appropriate to ! network to :i* x is connect$4 ,! in=mation 9 ! ,,ip head] :i* is us$ is prim>ily ! de/9ation address4 ,o!r in=mation 7e4g4 type ( s]vice7 is l>gely ignor$ at ?is "t4 ,! /ate ( ! network is det]m9$ by ! r\t]s pass+ in=mation among !mselves4 ,! di/ribution ( ! database 7:at ea* node kn[s71 ! =m ( ! updates1 & metrics us$ to measure ! value ( a connection1 are ! p>amet]s :i* det]m9e ! *>act]i/ics ( a r\t+ protocol4 ,"u "s algori?ms ea* node 9 ! network has complete k ( ! /ate ( ! network 7! adult algori?m74 ,?is implies ! nodes mu/ h l>g] am\nts ( local /orage & en\gh ,,cpu to se>* ! l>ge tables 9 a %ort en\gh "t 7rememb] ?is mu/ be done = ea* packet74 ,also1 r\t+ updates usually conta9 only *anges to ! exi/+ in=mation 7or y sp5d a l>ge am\nt ( ! network capacity pass+ ar\nd megabyte r\t+ updates74 ,?is type ( algori?m has sev]al problems4 ,s9ce ! only way ! r\t+ in=mation c be pass$ ar\nd is across ! network & ! propagation "t is non-trivial1 ! view ( ! network at ea* node is a correct hi/orical view ( ! network at v>y+ times 9 ! pa/4 7,! adult algori?m1 b r ?an look+ directly at ! d9+ area1 look+ at a photograph ( ! d9+ room4 ,"o is likely to pick ! optimal r\te & f9d a bus-c>t has mov$ 9 to block ! pa? aft] ! photo 0 tak574 ,^! inconsi/5cies c cause circul> r\tes 7call$ r\t+ loops7 :]e once a packet ent]s x is r\t$ 9 a clos$ pa? until its "t to live 7,,ttl7 field expires & x is disc>d$4 ,o!r algori?ms may "k ab\t only a subset ( ! network4 ,to prev5t loops 9 ^! protocols1 !y are usually us$ 9 a hi]>*ical network4 ,!y "k completely ab\t _! own area1 b to leave t area !y g to "o p>ticul> place 7! default gateway74 ,typically ^! are us$ 9 small] networks 7campus1 regional44474 -#aj- ,r\t+ protocols 9 curr5t use3 ,/atic 7no protocol-table_/default r\t+7 ,don't laugh4 ,x is probably ! mo/ reliable1 easie/ to implem5t1 & lea/ likely to get "o into tr\ble = a small network or a leaf on ! ,int]net4 ,?is is1 also1 ! only me?od available on "s ,,cpu-op]at+ sy/em comb9ations4 ,if a ho/ is connect$ to an ,e!rnet :i* has only "o gateway (f ( x1 "o %\ld make t ! default gateway = ! ho/ & d no o!r r\t+4 7,( c\rse t gateway may pass ! rea*ablity in=mation someh[ on ! o!r side ( itself74 ,"o ^w ( w>n+1 x is only ) extreme caution t "o %\ld use /atic r\tes 9 ! middle ( a network :i* is also us+ dynamic r\t+4 ,! r\t]s pass+ dynamic in=mation are sometimes confus$ by conflict+ dynamic & /atic r\tes4 ,if y\r ho/ is on an e!rnet ) multiple r\t]s to o!r networks on x & ! r\t]s are do+ dynamic r\t+ among !mselves1 x is usually bett] to take "p 9 ! dynamic r\t+ ?an to use /atic r\tes4 ,,rip ,,rip is a r\t+ protocol bas$ on ,,xns 7,x]ox ,network ,sy/em7 adapt$ = ,,ip networks4 ,x is us$ by _m r\t]s 7,proteon1 cisco1 ,,ub4447 & _m ,,bsd ,unix sy/ems ,,bsd sy/ems typically run a program call$ r\t$ to ex*ange in=mation ) o!r sy/ems runn+ ,,rip4 ,,rip works be/ = nets ( small diamet] :]e ! l9ks are ( equal spe$4 ,! reason = ?is is t ! metric us$ to det]m9e :i* pa? is be/ is ! hop-c\nt4 ,a hop is a trav]sal across a gateway4 ,s1 all ma*9es on ! same ,e!rnet are z]o hops away4 ,if a r\t] connects connects two net- works directly1 a ma*9e on ! o!r side ( ! r\t] is "o hop away4444 ,z ! r\t+ in=mation is pass$ ?r\gh a gateway1 ! gateway adds "o to ! hop c\nts to keep !m consi/5t across ! net- "w4 ,! diamet] ( a network is def9$ z ! l>ge/ hop-c\nt possible )9 a network4 ,un=- tunately1 a hop c\nt ( #af is def9$ z inf9ity 9 ,,rip mean+ ! l9k is d[n4 ,!re=e1 ,,rip w n all[ ho/s sep>at$ by m ?an #ae gateways 9 ! ,,rip space to communicate4 ,! o!r problem ) hop-c\nt metrics is t if l9ks h diff]5t spe$s1 t diff]5ce is n -#aa- reflect$ 9 ! hop-c\nt4 ,s a "o hop satellite l9k 7) a 4#e sec delay7 at #efkb w\ld be us$ in/ead ( a two hop ,t#a connection4 ,conge/ion c be view$ z a decrease 9 ! efficacy ( a l9k4 ,s1 z a l9k gets m conge/$1 ,,rip w /ill "k x is ! be/ hop-c\nt r\te & conge/ x ev5 m by ?r[+ m packets on ! queue = t l9k4 ,! protocol is n well docum5t$4 ,a gr\p ( p are work+ on produc+ an ,,rfc to bo? def9e ! curr5t ,,rip & to d "s ext5sions to x to all[ x to bett] cope ) l>g] networks4 ,curr5tly1 ! be/ docum5tation = ,,rip appe>s to be ! code to ,,bsd r\t$4 ,r\t$ ,! ,,r\t$ program1 :i* does ,,rip = #d4b;,,bsd sy/ems1 has _m options4 ,"o ( ! mo/ frequ5tly us$ is3 r\t$ -q 7quiet mode7 :i* means li/5 to ,,rip in=- mation b nev] broadca/ x4 ,?is w\ld be us$ by a ma*9e on a network ) multiple ,,rip speak+ gate- ways4 ,x all[s ! ho/ to det]m9e :i* gateway is be/ 7hopwise7 to use to rea* a di/ant network4 7,( c\rse y might want to h a default gateway to prev5t hav+ to pass all ! addresses kn[n to ! ,int]net ar\nd ) ,,rip74 ,!re are two ways to ins]t /atic r\tes into r\t$1 ! _/etc_/gateways file & ! r\te add comm&4 ,/atic r\tes are useful if y "k h[ to rea* a di/ant network1 b y are n receiv+ t r\te us+ ,,rip4 ,= ! mo/ "p ! r\te add comm& is pref]able to use4 ,! reason = ?is is t ! comm& adds ! r\te to t ma*9e's r\t+ table b does n export x ?r\gh ,,rip4 ,! _/etc_/gateways file takes prec$5ce ov] any r\t+ in=mation receiv$ ?r\gh a ,,rip update4 ,x is also broadca/ z fact 9 ,,rip updates produc$ by ! ho/ )\t "q1 s if a mi/ake is made 9 ! _/etc_/gateways file1 t mi/ake w soon p]meate ! ,,rip space & may br+ ! network to its knees4 ,"o ( ! problems ) r\t$ is t y h v little control ov] :at gets broadca/ & :at doesn't4 ,_m times 9 l>g] networks :]e v>i\s p>ts ( ! network are "u diff]5t adm9i/rative controls1 y w\ld l to pass on ?r\gh ,,rip only nets :i* y receive f ,,rip & y "k are reasonable4 ,?is prev5ts p f add+ ,,ip addresses to ! network :i* may be illegal & y be+ responsible = pass+ !m on to ! ,int]net4 ,?is -#ab- type ( reasonability *ecks are n available ) r\t$ & leave x usable1 b inadequate = l>ge networks4 ,hello 7,,rfc-#hia7 ,hello is a r\t+ protocol :i* 0 design$ & implem5t$ 9 a exp]im5tal s(tw>e r\t] call$ a ,fuzzball :i* runs on a ,,pdp-#aa4 ,x does n h wide usage1 b is ! r\t+ protocol curr5tly us$ on ! ,n,s,fnet backbone4 ,! data transf]r$ betwe5 nodes is simil> to ,,rip 7a li/ ( networks & _! metrics74 ,! metric1 h[ev]1 is milliseconds ( delay4 ,?is all[s ,hello to be us$ ov] nets ( v>i\s l9k spe$s & p]=ms bett] 9 conge/ive situations4 ,"o ( ! mo/ int]e/+ side effects ( ,hello bas$ networks is _! great timekeep+ ability4 ,if y consid] ! problem ( measur+ delay on a l9k = ! metric1 y f9d t x is n an easy ?+ to d4 ,y _c measure r\nd trip "t s9ce ! return l9k may be m conge/$1 ( a diff]5t spe$1 or ev5 n !re4 ,x is n really feasible = ea* node on ! network to h a built9 ,,wwv 7nationwide radio "t /&>d7 receiv]4 ,s1 y mu/ design an algori?m to pass ar\nd "t betwe5 nodes ov] ! network l9ks :]e ! delay 9 transmission c only be approximat$4 ,hello r\t]s d ?is & 9 a nationwide network ma9ta9 syn*roniz$ "t )9 milliseconds4 ,ext]ior ,gateway ,protocol 7,,egp ,,rfc-#ijd7 ,,egp is n /rictly a r\t+ protocol1 x is a rea*a- bility protocol4 ,x tells only if nets c be rea*$ ?r\gh a p>ticul> gateway1 n h[ good ! connec- tion is4 ,x is ! /&>d by :i* gateways to local nets in=m ! ,a,r,p,anet ( ! nets !y c rea*4 ,!re is a metric pass$ ar\nd by ,,egp b its usage is n /&>diz$ =mally4 ,its typical value is value is #a to #h :i* are arbitr>y goodness ( l9k values und]/ood by ! int]nal ,,ddn gateways4 ,! small] ! value ! bett] & a value ( #h be+ unrea*- able4 ,a quirk ( ! protocol prev5ts di/+ui%+ betwe5 #a & #b1 #c & #d4441 s ! usablity ( ?is z a metric is z ?ree values & unrea*able4 ,)9 ,n,s,fnet ! values us$ are #a1 #c1 & unrea*able4 ,_m r\t]s talk ,,egp s !y c be us$ = ,a,r,p,anet gateways4 -#ac- ,gat$ ,s we h regional & campus networks talk+ ,,rip among !mselves1 ! ,n,s,fnet backbone talk+ ,hello1 & ! ,,ddn speak+ ,,egp4 ,h[ d !y int]op]ate8 ,9 ! beg9n+ !re 0 /atic r\t+1 assembl$ into ! ,fuzzball s(tw>e configur$ = ea* site4 ,! problem ) do+ /atic r\t+ 9 ! middle ( ! network is t x is broadca/ to ! ,int]net :e!r x is usable or n4 ,!re=e1 if a net becomes unrea*able & y try to get !re1 dynamic r\t+ w imm$iately issue a net unrea*able to y4 ,"u /atic r\t+ ! r\t]s w\ld ?9k ! net c\ld be rea*$ & w\ld cont9ue try+ until ! application gave up 79 #b or m m9utes74 ,m>k ,f$or ( ,cornell 7f$ordevvax4tn4cornell4edu7 attempt$ to solve ^! problems ) a replacem5t = r\t$ call$ gat$4 ,gat$ talks ,,rip to ,,rip speak+ ho/s1 ,,egp to ,,egp speak]s1 & ,hello to ,hello'ers4 ,^! speak]s frequ5tly all live on "o ,e!rnet1 b luckily 7or unluckily7 _c und]/& ea* o!rs rum9ations4 ,9 addition1 "u configuration file control x c filt] ! conv]sion4 ,= example1 "o c produce a configuration say+ ann\nce ,,rip nets via ,hello only if !y are specifi$ 9 a li/ & are rea*able by way ( a ,,rip broadca/ z well4 ,?is means t if a rogue network appe>s 9 y\r local site's ,,rip space1 x won't be pass$ ?r\gh to ! ,hello side ( ! _w4 ,!re are also configuration options to d /atic r\t+ & "n tru/$ gateways4 ,?is may s\nd l ! greate/ ?+ s9ce slic$ bread1 b !re is a cat* call$ metric conv]sion4 ,y h ,,rip measur+ 9 hops1 ,hello measur+ 9 milliseconds1 & ,,egp us+ arbitr>y small numb]s4 ,! big que/ions is h[ _m hops to a millisecond1 h[ _m milliseconds 9 ! ,,egp numb] #c4444 ,also1 rememb] t inf9ity 7unrea*ability7 is #af to ,,rip1 #cjjjj or s to ,hello1 & #h to ! ,,ddn ) ,,egp4 ,gett+ all ^! metrics to "w well toge!r is no small feat4 ,if done incorrectly & y translate an ,,rip ( #af into an ,,egp ( #f1 ev]yone 9 ! ,a,r,p,anet w /ill ?9k y\r gateway c rea* ! unrea*able & w s5d e packet 9 ! _w y\r way4 ,= ^! reasons1 ,m>k reque/s t y consult closely ) him :5 configur+ & us+ gat$4 -#ad- ,names ,all r\t+ across ! network is done by means ( ! ,,ip address associat$ ) a packet4 ,s9ce humans f9d x difficult to rememb] addresses l #abh4agd4e4ej1 a symbolic "n regi/] 0 set up at ! ,,nic :]e p w\ld say ,i w\ld l my ho/ to be nam$ 'uiucuxc'4 ,ma*9es connect$ to ! ,int]net across ! nation w\ld connect to ! ,,nic 9 ! middle ( ! night1 *eck modification dates on ! ho/s file1 & if modifi$ move x to _! local ma*9e4 ,) ! adv5t ( work/ations & micros1 *anges to ! ho/ file w\ld h to be made nightly4 ,x w\ld also be v labor int5sive & consume a lot ( network b&wid?4 ,,rfc-#hhb & a numb] ( o!rs describe doma9 "n s]vice1 a di/ribut$ data base sy/em = mapp+ names into addresses4 ,we mu/ look a little m closely into :at's 9 a "n4 ,fir/1 note t an address specifies a p>ticul> connec- tion on a specific network4 ,if ! ma*9e moves1 ! address *anges4 ,second1 a ma*9e c h "o or m names & "o or m network addresses 7connections7 to diff]5t networks4 ,names po9t to a some?+ :i* does useful "w 7i4e4 ! ma*9e7 & ,,ip addresses po9t to an int]face on t provid]4 ,a "n is a purely symbolic repres5tation ( a li/ ( addresses on ! network4 ,if a ma*9e moves to a diff]5t network1 ! addresses w *ange b ! "n c\ld rema9 ! same4 ,doma9 names are tree /ructur$ names ) ! root ( ! tree at ! "r4 ,= example3 uxc4cso4uiuc4edu is a ma*9e call$ 'uxc' 7purely arbitr>y71 )9 ! subdoma9s me?od ( allocation ( ! ,u ( ,i7 & 'uiuc' 7! ,univ]sity ( ,ill9ois at ,urbana71 regi/]$ ) 'edu' 7! set ( educational in/itutions74 ,a simplifi$ model ( h[ a "n is resolv$ is t on ! us]'s ma*9e !re is a resolv]4 ,! resolv] kn[s h[ to contact across ! network a root "n s]v]4 ,root s]v]s are ! base ( ! tree /ructur$ data retrieval sy/em4 ,!y "k :o is responsible = h&l+ fir/ level doma9s 7e4g4 'edu'74 ,:at root s]v]s to use is an in/allation p>amet]4 ,f ! root s]v] ! resolv] f9ds out :o provides 'edu' s]vice4 ,x contacts ! 'edu' "n s]v] :i* supplies x ) a li/ ( addresses ( s]v]s = ! subdoma9s 7l 'uiuc'74 ,?is action is repeat$ ) ! subdoma9 s]v]s until ! f9al sub- doma9 returns a li/ ( addresses ( int]faces on ! ho/ 9 "q4 ,! us]'s ma*9e !n has its *oice ( :i* ( ^! addresses to use = communication4 -#ae- ,a gr\p may apply = its own doma9 "n 7l 'uiuc' above74 ,?is is done 9 a mann] simil> to ! ,,ip address allocation4 ,! only requirem5ts are t ! reque/or h two ma*9es rea*able f ! ,int]net1 :i* w act z "n s]v]s = t doma94 ,^? s]v]s c\ld also act z s]v]s = subdoma9s or o!r s]v]s c\ld be designat$ z su*4 ,note t ! s]v]s ne$ n be locat$ 9 any p>ticul> place1 z long z !y are rea*- able = "n resolution4 7,u ( ,i c\ld ask ,mi*igan ,/ate to act on its behalf & t w\ld be f9e74 ,! bigge/ problem is t someone mu/ d ma9t5ance on ! database4 ,if ! ma*9e is n conv5i5t1 t might n be done 9 a timely fa%ion4 ,! o!r ?+ to note is t once ! doma9 is allocat$ to an adm9i/rative entity1 t entity c freely allocate subdoma9s us+ :at ev] mann] x sees fit4 ,! ,b]keley ,int]net ,"n ,doma9 7,,b9d7 ,s]v] implem5ts ! ,int]net "n s]v] = ,,unix sy/ems4 ,! "n s]v] is a di/ribut$ data base sy/em t all[s cli5ts to "n res\rces & to %>e t in=mation ) o!r net- "w ho/s4 ,,b9d is integrat$ ) #d4c;,,bsd & is us$ to lookup & /ore ho/ names1 addresses1 mail ag5ts1 ho/ in=mation1 & m4 ,x replaces ! _/etc_/ho/s file = ho/ "n lookup4 ,,b9d is /ill an evolv+ program4 ,to keep up ) reports on op]ational problems1 future design decisions1 etc1 jo9 ! ,,b9d mail+ li/ by s5d+ a reque/ to b9d-reque/ucb>p4,b]keley4,,edu4 ,,b9d c also be obta9$ via anonym\s ,,ftp f ucb>pa4b]kley4edu4 ,!re are sev]al advantages 9 us+ ,,b9d4 ,"o ( ! mo/ important is t x frees a ho/ f rely+ on _/etc_/ho/s be+ up to date & complete4 ,)9 ! 4uiuc4edu doma91 only a few ho/s are includ$ 9 ! ho/ table di/ribut$ by ,,sri4 ,! rema9d] are li/$ locally )9 ! ,,b9d tables on uxc4cso4uiuc4edu 7! s]v] ma*9e = mo/ ( ! 4uiuc4edu doma974 ,all are equally rea*able f any o!r ,int]net ho/ runn+ ,,b9d4 ,,b9d c also provide mail =w>d+ in=mation = inte- rior ho/s n directly rea*able f ! ,int]net4 ,^! ho/s c ei!r be on non-adv]tis$ networks1 or n con- nect$ to a network at all1 z 9 ! case ( ,,uucp-rea*able ho/s4 ,m in=mation on ,,b9d is available 9 ! ,"n ,s]v] ,op]ations ,guide = ,,b9d 9 ,,unix ,sy/em ,manag]'s ,manual1 #d4c;,,bsd release4 ,!re are a few special doma9s on ! network1 l ,,sri- ,,nic4,,arpa4 ,! 'arpa' doma9 is hi/orical1 ref]r+ to ho/s regi/]$ 9 ! old ho/s database at ! ,,nic4 ,!re are o!rs ( ! =m ,,nnsc4,,nsf4,,net4 ,^! special doma9s are us$ sp>+ly & require ample ju/ification4 ,!y ref] to s]v]s "u ! adm9i/rative control ( -#af- ! network r ?an any s+le organization4 ,?is all[s = ! actual s]v] to be mov$ ar\nd ! net :ile ! us] int]face to t ma*9e rema9s con/ant4 ,t is1 %\ld ,,bbn rel9qui% control ( ! ,,nnsc1 ! new provid] w\ld be po9t$ to by t "n4 ,9 actuality1 ! doma9 sy/em is a mu* m g5]al & complex sy/em ?an has be5 describ$4 ,resolv]s & "s s]v]s ca*e in=mation to all[ /eps 9 ! resolution to be skipp$4 ,in=mation provid$ by ! s]v]s c be arbitr>y1 n m]ely ,,ip addresses4 ,?is all[s ! sy/em to be us$ bo? by non-,,ip networks & = mail1 :]e x may be necess>y to give in=mation on int]m$iate mail bridges4 ,:at's wrong ) ,b]keley ,unix ,univ]sity ( ,cali=nia at ,b]keley has be5 fund$ by ,,d>pa to modify ! ,unix sy/em 9 a numb] ( ways4 ,includ$ 9 ^! modifications is support = ! ,int]net protocols4 ,9 e>li] v]sions 7e4g4 ,,bsd #d4b7 !re 0 good support = ! basic ,int]net protocols 7,,tcp1 ,,ip1 ,,smtp1 ,,arp7 :i* all[$ x to p]=m nicely on ,,ip e!r- nets & small] ,int]nets4 ,!re 7 defici5cies1 h[- ev]1 :5 x 0 connect$ to complicat$ networks4 ,mo/ ( ^! problems h be5 resolv$ "u ! newe/ release 7,,bsd #d4c74 ,s9ce x is ! spr+bo>d f :i* _m v5dors h laun*$ ,unix implem5tations 7ei!r by port+ ! exi/+ code or by us+ x z a model71 _m implem5tations 7e4g4 ,ultrix7 are /ill bas$ on ,,bsd #d4b4 ,!re=e1 _m implem5tations /ill exi/ ) ! ,,bsd #d4b problems4 ,z "t goes on1 :5 ,,bsd #d4c trickles ?r\gh v5dors z new release1 _m ( ! problems w be resolv$4 ,foll[+ is a li/ ( "s problem sc5>ios & _! h&l+ "u ea* ( ^! releases4 ,,icmp r$irects ,"u ! ,int]net model1 all a sy/em ne$s to "k to get any:]e 9 ! ,int]net is its own address1 ! address ( :]e x wants to g1 & h[ to rea* a gateway :i* kn[s ab\t ! ,int]net4 ,x doesn't h to be ! be/ gateway4 ,if ! sy/em is on a network ) multiple gateways1 & a ho/ s5ds a packet = deliv]y to a gateway :i* feels ano!r directly connect$ gateway is m appropriate1 ! gateway s5ds ! s5d] a message4 ,?is message is an ,,icmp r$irect1 :i* politely says ,i'll deliv] ?is message = y1 b y really ought to use t gate- way ov] !re to rea* ?is ho/4 ,,bsd #d4b ignores ^! messages4 ,?is creates m /ress on ! gate- ways & ! local network1 s9ce = e packet -#ag- s5t1 ! gateway s5ds a packet to ! orig9ator4 ,,bsd #d4c uses ! r$irect to update its r\t+ tables1 w use ! r\te until x times out1 !n rev]t to ! use ( ! r\te x ?9ks is %\ld use4 ,! :ole process !n repeats1 b x is f> bett] ?an "o p] packet4 ,trail]s ,an application 7l ,,ftp7 s5ds a /r+ ( octets to ,,tcp :i* breaks x into *unks1 & adds a ,,tcp head]4 ,,tcp !n s5ds blocks ( data to ,,ip :i* adds its own head]s & %ips ! packets ov] ! network4 ,all ?is prep5d+ ( ! data ) head]s causes memory moves 9 bo? ! s5d+ & ! receiv+ ma*9es4 ,someone got ! bright idea t if packets 7 long & !y /uck ! head]s on ! end 7!y became trail]s71 ! receiv+ ma*9e c\ld put ! packet on ! beg9n+ ( a page b\nd>y & if ! trail] 0 ,,ok m]ely delete x & transf] control ( ! page ) no memory moves involv$4 ,! problem is t trail]s 7 nev] /&>diz$ & mo/ gateways don't "k to look = ! r\t+ in=mation at ! end ( ! block4 ,:5 trail]s are us$1 ! ma*9e typically works f9e on ! local network 7no gateways involv$7 & = %ort blocks ?r\gh gateways 7on :i* trail]s ar5't us$74 ,s ,,telnet & ,,ftp's ( v %ort files "w j f9e & ,,ftp's ( long files seem to hang4 ,on ,,bsd #d4b trail]s are a boot option & "o %\ld make sure !y are (f :5 us+ ! ,int]net4 ,,bsd #d4c negotiates trail]s1 s x uses !m on its local net & doesn't use !m :5 go+ across ! network4 ,retransmissions ,,tcp fires (f blocks to its p>tn] at ! f> end ( ! connection4 ,if x doesn't receive an ackn[l$ge- m5t 9 a reasonable am\nt ( "t x retransmits ! blocks4 ,! det]m9ation ( :at is reasonable is done by ,,tcp's retransmission algori?m4 ,!re is no correct algori?m b "s are bett] ?an o!rs1 :]e bett] is measur$ by ! numb] ( retransmis- sions done unnecess>ily4 ,,bsd #d4b _h a retransmission algori?m :i* retransmitt$ quickly & (t54 ,?is is exactly :at y w\ld want if y _h a bun* ( ma*9es on an e!rnet 7a l[ delay network ( l>ge b&wid?74 ,if y h a network ( relatively long] delay & sc>ce b&wid? 7e4g4 #efkb l9es71 x t5ds to retransmit too aggressively4 ,!re=e1 x makes ! networks & gateways pass m traffic ?an is really necess>y = a giv5 conv]sation4 ,retransmis- sion algori?ms d adapt to ! delay ( ! network -#ah- aft] a few packets1 b #d4b's adapts sl[ly 9 delay situations4 ,,bsd #d4c does a lot bett] & tries to d ! be/ = bo? worlds4 ,x fires (f a few retransmissions really quickly assum+ x is on a l[ delay network1 & !n backs (f v quickly4 ,x also all[s ! delay to be ab\t #d m9utes be=e x gives up & decl>es ! connection brok54 -#ai- ,app5dix ,a ,ref]5ces to ,rem$ial ,in=mation ,quat]man & ,hosk9s1 ,notable ,comput] ,networks1 ,communications ( ! ,,acm1 ,vol #bi1 #aj1 pp4 #icb-iga 7,octob]1 #aihf74 ,tann5baum1 ,&rew ,s41 ,comput] ,networks1 ,pr5tice ,hall1 #aiha4 ,h$rick1 ,*uck1 ,introduction to ! ,int]net ,protocols1 ,anonym\s ,,ftp f topaz4rutg]s4edu1 directory pub_/tcp-ip-docs1 file tcp-ip-intro4doc4 -#bj- ,app5dix ,b ,li/ ( ,major ,r,f,cs ,,rfc-#gfh ,us] ,datagram ,protocol 7,,udp7 ,,rfc-#gia ,int]net ,protocol 7,,ip7 ,,rfc-#gib ,int]net ,control ,message ,protocol 7,,icmp7 ,,rfc-#gic ,transmission ,control ,protocol 7,,tcp7 ,,rfc-#hba ,simple ,mail ,transf] ,protocol 7,,smtp7 ,,rfc-#hbb ,/&>d = ! ,=mat ( ,,arpa ,int]net ,text ,messages ,,rfc-#hed ,telnet ,protocol ,,rfc-#iag 99 ,int]net ,subnets ,,rfc-#iai 99 ,broadca/+ ,int]net ,datagrams ,,rfc-#ibb 99 ,broadca/+ ,int]net ,datagrams 9 ! ,pres5ce ( ,subnets ,,rfc-#idj 99 ,t[>d an ,int]net ,/&>d ,s*eme = ,subnett+ ,,rfc-#idg 99 ,multi-network ,broadca/+ )9 ! ,int]net ,,rfc-#iej 99 ,int]net ,/&>d ,subnett+ ,proc$ure ,,rfc-#iei ,file ,transf] ,protocol 7,,ftp7 ,,rfc-#iff 99 ,ho/ ,gr\ps3 ,a ,multica/ ,ext5sion to ! ,int]net ,protocol ,,rfc-#ihh 99 ,ho/ ,ext5sions = ,,ip ,multica/+ ,,rfc-#iig 99 ,int]net ,numb]s ,,rfc-#ajaj 99 ,assign$ ,numb]s ,,rfc-#ajaa 99 ,(ficial ,,arpa-,int]net ,protocols ,,rfc's m>k$ ) ! a/]isk 7997 are n includ$ 9 ! #aihe ,,ddn ,protocol ,h&book4 ,note3 ,?is li/ is a portion ( a li/ ( ,,rfc's by topic retriev$ f ! ,,nic "u ,,net9fo3,,rfc-,,sets4,,txt 7anonym\s ,,ftp ( c\rse74 ,! foll[+ li/ is n necess>y = connection to ! ,int]net1 b is useful 9 und]/&+ ! doma9 sy/em1 mail sy/em1 & gateways3 ,,rfc-#hhb ,doma9 ,names - ,concepts & ,facilities ,,rfc-#hhc ,doma9 ,names - ,implem5tation ,,rfc-#igc ,doma9 ,sy/em ,*anges & ,obs]vations ,,rfc-#igd ,mail ,r\t+ & ! ,doma9 ,sy/em ,,rfc-#ajji ,requirem5ts = ,int]net ,gateways -#ba- ,app5dix ,c ,contact ,po9ts = ,network ,in=mation ,network ,in=mation ,c5t] 7,,nic7 ,,ddn ,network ,in=mation ,c5t] ,,sri ,int]national1 ,room ,,ej#bia #ccc ,rav5swood ,av5ue ,m5lo ,p>k1 ,,ca #idjbe 7#hjj7 #bce-caee or 7#dae7 #hei-cfie ,,nic,,sri-,,nic4,,arpa ,,nsf ,network ,s]vice ,c5t] 7,,nnsc7 ,,nnsc ,,bbn ,laboratories ,inc4 #aj ,m\lton ,/4 ,cambridge1 ,,ma #jbbch 7#fag7 #dig-cdjj ,,nnsc,,nnsc4,,nsf4,,net -#bb- ,gloss>y core gateway ,! inn]mo/ gateways ( ! ,a,r,p,anet4 ,^! gateways h a total picture ( ! rea*a- bility to all networks kn[n to ! ,a,r,p,anet ) ,,egp4 ,!y !n r$i/ribute rea*abil- ity in=mation to all ^? gateways speak- + ,,egp4 ,x is f !m y\r ,,egp ag5t 7!re is "o act+ = y some:]e if y c rea* ! ,a,r,p,anet7 f9ds out x c rea* all ! nets on ! ,a,r,p,anet4 ,:i* is !n pass$ to y via ,hello1 gat$1 ,,rip4444 c\nt to inf9ity ,! symptom ( a r\t+ problem :]e r\t+ in=mation is pass$ 9 a circul> mann] ?r\gh multiple gateways4 ,ea* gate- way increm5ts ! metric appropriately & passes x on4 ,z ! metric is pass$ ar\nd ! loop1 x increm5ts to ev] increas+ values til x rea*es ! maximum = ! r\t+ protocol be+ us$1 :i* typically d5otes a l9k outage4 hold d[n ,:5 a r\t] discov]s a pa? 9 ! network has gone d[n ann\nc+ t t pa? is d[n = a m9imum am\nt ( "t 7usually at lea/ two m9utes74 ,?is all[s = ! pro- pagation ( ! r\t+ in=mation across ! network & prev5ts ! =mation ( r\t+ loops4 split horizon ,:5 a r\t] 7or gr\p ( r\t]s work+ 9 consort7 accept r\t+ in=mation f mul- tiple ext]nal networks1 b d n pass on in=mation le>n$ f "o ext]nal network to any o!rs4 ,?is is an attempt to prev5t bogus r\tes to a network f be+ propagat$ because ( gossip or c\nt+ to inf9ity4 -#bc-