Overview Chter NETWORK LYER Distributed Comuting Grou Comuter Networks Winter 2002 / 2003 Network lyer servies Routing rinile: th seletion Hierrhil routing, slbility IP, the Internet Protool Internet routing rotools relible trnsfer Intr-domin Inter-domin Routing onvergene Wht s inside router? dvned Tois IPv6 Distributed Comuting Grou Comuter Networks R. Wttenhofer /2 Network lyer funtions Network servie model Trnsort ket from sending to reeiving hosts Network lyer rotools in every host, router lition trnsort dt link hysil Three imortnt funtions: th determintion: route tken by kets from soure to destintion. There re vrious routing lgorithms swithing: move kets from router s inut to rorite router outut ll setu: some rhitetures require router ll setu long th before dt flows dt link hysil dt link hysil dt link hysil dt link hysil dt link hysil dt link hysil dt link hysil dt link hysil lition trnsort dt link hysil Q: Wht servie model for hnnel trnsorting kets from sender to reeiver? gurnteed bndwidth? reservtion of inter-ket timing (no jitter)? loss-free delivery? in-order delivery? ongestion feedbk to sender? servie bstrtion The most imortnt bstrtion rovided by lyer:? virtul iruit? or? dtgrm? Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 Distributed Comuting Grou Comuter Networks R. Wttenhofer /
Virtul iruits Virtul iruits: signling rotools soure-to-destintion th behves muh like telehone iruit erformne-wise tions long soure-to-destintion th used to setu, mintin, nd terdown VC used in TM, frme-rely, X.25 not used in tody s Internet ll setu, terdown for eh ll before dt n flow eh ket rries VC identifier (not destintion host ID) every router on soure-dest th mintins stte for eh ssing onnetion trnsort-lyer onnetion only involved two end systems link, router resoures (bndwidth, buffers) my be lloted to VC to get iruit-like erformne lition trnsort dt link hysil 5. Dt flow begins 6. Reeive dt. Cll onneted 3. et ll. Initite ll 2. inoming ll lition trnsort dt link hysil Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 Distributed Comuting Grou Comuter Networks R. Wttenhofer /6 Dtgrm s: The Internet model Network lyer servie models no ll setu t lyer routers: no stte bout end-to-end onnetions no -level onet of onnetion kets tyilly routed using destintion host ID kets between sme soure-dest ir my tke different ths lition trnsort dt link hysil. Send dt 2. Reeive dt lition trnsort dt link hysil Network rhiteture Internet TM TM TM TM Servie Model best effort CBR VBR BR UBR Bndwidth none onstnt rte gurnteed rte gurnteed minimum none Gurntees? Loss Order Timing no yes yes no no no yes yes yes yes no yes yes no no Congestion feedbk no (inferred vi loss) no ongestion no ongestion yes no Distributed Comuting Grou Comuter Networks R. Wttenhofer /7 Distributed Comuting Grou Comuter Networks R. Wttenhofer /8
Dtgrm or VC : why? Routing Internet dt exhnge mong omuters elsti servie, no strit timing req. smrt end systems (omuters) n dt, erform ontrol, error reovery simle inside, omlexity t edge mny link tyes different hrteristis uniform servie diffiult TM evolved from telehony humn onverstion strit timing, relibility requirements need for gurnteed servie dumb end systems telehones omlexity inside Routing rotool Gol: determine good th (sequene of routers) through from soure to dest. Grh bstrtion for routing grh nodes re routers grh edges re hysil links link ost: dely, $ ost, or ongestion level 2 5 B D 2 3 3 C E 5 F 2 good th: tyilly mens minimum ost th other definitions ossible Distributed Comuting Grou Comuter Networks R. Wttenhofer /9 Distributed Comuting Grou Comuter Networks R. Wttenhofer /0 Routing lgorithm lssifition Single Soure Shortest Pths Globl or deentrlized? Globl ll routers hve omlete toology, link ost info link stte lgorithms Deentrlized router knows hysillyonneted neighbors, link osts to neighbors itertive roess of omuttion, exhnge of info with neighbors distne vetor lgorithms Stti or dynmi? Stti routes hnge slowly over time Dynmi routes hnge more quikly eriodi udte in resonse to link ost hnges For given soure we wnt the shortest th to ll other nodes Otimlity rinile For eh shortest th = (v 0, v,, v k ), eh subth = (v i,, v j ) is lso shortest th. If this wsn t the se then there ws shorter th from v i to v j whih one ould use to shortut th. For given soure s nd node v this mens There is node u suh tht (s(s,u)) + (u,v) = (s(s,v)), tht is, in generl (s(s,u )) + (u,v) (s(s,v)). The single soure shortest th roblem results in tree Distributed Comuting Grou Comuter Networks R. Wttenhofer / Distributed Comuting Grou Comuter Networks R. Wttenhofer /2
Single soure shortest th: Intuition lgorithm ide One uon time, the Chinese Emeror wnted to know the distne nd the best routes from Beijing to ll the mjor ities in his ountry. t the first dy of the summer, few souts strted in Beijing, tking ll the rods leving Beijing. Whenever sout rrives first in ity, he notes the urrent time nd the th he took, nd then immeditely reruits new souts tht leve the ity, tking ll the ossible rods nd trils. Then he returns to Beijing. Whenever sout rrives seond (or lter) in ity, he does nothing nd returns to Beijing. This lgorithm solves the single soure shortest th roblem How n one rove tht it is orret? How effiient is the lgorithm? There re 3 grous of nodes in the To the green nodes we know the shortest th The blue nodes re diretly rehble from the green nodes ll other nodes re blk Ide v Strt with w soure s s the only green node u Color the best* blue s node green, one fter nother, until ll nodes re green (*best = minimum distne to soure s of ll blue nodes) x Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 Distributed Comuting Grou Comuter Networks R. Wttenhofer / Link-Stte Routing lgorithm Dijkstr s lgorithm (for soure s nd edge osts ) Dijkstr s lgorithm net toology, link osts known to ll nodes omlished vi link stte brodst ll nodes hve sme info omutes single-soure shortest th tree gives routing tble for soure Nottion (i,j): link ost from node i to j. Cn be infinite if not diret neighbors, osts define djeny mtrix v.distne: urrent vlue of ost of th from soure s to destintion v v.visited: boolen vrible tht determines if otiml th to v ws found v.red: the redeessor node of v in the routing tree B: the set of blue nodes s.visited := true; s.distne := 0; s.red := s; // init soure s for ll nodes v V \ s do // init ll other nodes v.visited := flse; v.distne := ; v.red := undefined; B := {} // B is the set of blue nodes, initilly ll neighbors of s for ll nodes v V \ s tht re diret neighbors of s B := B + {v}; v.distne := (s,v); v.red := s; while B not emty do // lwys hoose the best blue node v v := node in B with minimum v.distne; B := B {v}; v.visited := true; for ll neighbors w of v with w.visited = flse; // udte neighbors of v if w not in B then B := B + {w}; w.distne := v.distne+(v,w); w.red := v; if w B then if (v.distne+(v,w) < w.distne) then w.distne := v.distne+(v,w); w.red := v; endwhile Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 Distributed Comuting Grou Comuter Networks R. Wttenhofer /6
Dijkstr s lgorithm: exmle Dijkstr s lgorithm, lgorithm omlexity Ste 0 2 3 5 visited, D () D, E (2) DE, B (2) DEB, C (3) DEBC, F () Set of blue nodes B (with distne) D (), B (2), C (5) E (2), B (2), C () B (2), C (3), F() C (3), F() F() - n nodes, m (direted) edges Initiliztion osts O(n) oertions Eh round in the loo visits one unvisited node, tht is, there re extly n- rounds. In eh round you hve to find nd remove the minimum node distne node v, nd udte the neighbors of node v. You n do both stes in O(n) time, thus O(n 2 ) totl time. 2 5 B 2 D 3 3 C E 5 F 2 Remrk : With Fiboni-He, one n imlement the whole lgorithm in O(m + n log n) time. Remrk 2: Some books lim tht the lgorithm omlexity is O(n log n), whih is lerly bogus sine t lest ll the edges hve to be exmined Distributed Comuting Grou Comuter Networks R. Wttenhofer /7 Distributed Comuting Grou Comuter Networks R. Wttenhofer /8 Dijkstr s lgorithm, orretness Distne Vetor Routing: Intuition Osilltions ossible For exmle if link osts deend on the mount of rried trffi. Exmle: three flows to node, with trffi,, nd e (<) Genev +e D 0 0 B 0 e C e initilly 2+e 0 D +e B 0 0 C B nd C hve better routes 0 2+e D 0 0 B C +e D, C, B hve better routes How would you rove tht Dijkstr s lgorithm is otiml for onstnt (nd ositive!) link osts? (Not in this ourse.) 2+e 0 D +e B 0 e C et. b Routing Tble of b Destintion Dir Genev Distributed Comuting Grou Comuter Networks R. Wttenhofer /9 Distributed Comuting Grou Comuter Networks R. Wttenhofer /20
Distne Vetor Routing Distne Vetor Routing lgorithm Distne : 7 Distne : 5!? Distne : 3 b Distne : Destintion Dir Dst Genev 0 lgorithm is itertive ontinues until no nodes exhnge info self-terminting: no signl to sto synhronous nodes need not to iterte in lok-ste distributed eh node ommunites only with diret neighbors Routing Tble with distne info eh node hs one node x hs for eh neighbor z n entry for eh destintion y (s in exmle before); D x (y,z) = distne from x to y through z the best route for given destintion is mrked Distributed Comuting Grou Comuter Networks R. Wttenhofer /2 Distributed Comuting Grou Comuter Networks R. Wttenhofer /22 Distne Vetor lgorithm: exmle Distne tble gives routing tble E D () ost to destintion vi B D Outgoing link to use, ost 2 X Y 7 Z destintion B C D 7 6 8 9 5 5 2 destintion B C D, D,5 D, D,2 7 B E 8 2 C D 2 Distne tble Routing tble Distributed Comuting Grou Comuter Networks R. Wttenhofer /23 Distributed Comuting Grou Comuter Networks R. Wttenhofer /2
Distne Vetor Routing Count to Infinity Problem Lol itertion used by lol link ost hnge Neighbor sends messge sying tht (t lest) one of its lest ost ths hnged lgorithm is distributed eh node notifies neighbors only when its lest ost th to ny destintion hnges neighbors then notify their neighbors if neessry, et. Eh node exeutes loo: wit for (hnge in lol link ost or msg from neighbor) reomute distne tble if lest ost th to ny dest hs hnged, notify ll neighbors : 2 : b : 3 : : 5 : 6 : 7 : 8 Distributed Comuting Grou Comuter Networks R. Wttenhofer /25 Distributed Comuting Grou Comuter Networks R. Wttenhofer /26 Distne Vetor: link ost hnges Distne Vetor: link ost hnges Link ost hnges node detets lol link ost hnge udtes distne tble if ost hnge in lest ost th, notify neighbors X Y 50 Z Wht if the ost of link grows? Comre with the ount to infinity roblem (More on this lter) 60 X Y 50 Z good news trvel fst lgorithm termintes lgorithm ontinues on! Distributed Comuting Grou Comuter Networks R. Wttenhofer /27 Distributed Comuting Grou Comuter Networks R. Wttenhofer /28
Link-Stte vs. Distne-Vetor Routing lgorithms Hierrhil Routing Messge omlexity LS: with n nodes, m links, flooded with O(nm) messges DV: exhnge between neighbors only onvergene time vries Seed of Convergene LS: O(m + n log n) my hve osilltions DV: onvergene time vries ount-to-infinity roblem (lter more) Robustness wht hens if router mlfuntions? LS: node n dvertise inorret link ost eh node omutes only its own tble DV: DV node n dvertise inorret th ost eh node s tble used by others errors rogte thru So fr we studied ideliztion ll routers identil, flt grh Relity Internet is of s Eh dmin my wnt to ontrol routing in own You nnot store 200 million destintions in (ll) routing tbles; routing tble exhnge too mssive Ide ggregte routers into grous, utonomous systems (S) routers in sme S run sme routing rotool intr-s routing rotool routers in different S n run different intr-s routing rotool Seil gtewy routers in S s run intr-s routing rotool with ll other routers in S run inter-s routing rotool with other gtewy routers Distributed Comuting Grou Comuter Networks R. Wttenhofer /29 Distributed Comuting Grou Comuter Networks R. Wttenhofer /30 Intr-S nd Inter-S routing Intr-S nd Inter-S routing C C.b b d. b inter-s, intr-s routing in gtewy.. B. B b Gtewys: erform inter-s routing mongst themselves erform intr-s routers with other routers in their S lyer link lyer hysil lyer Host h C C.b b.. d b Intr-S routing within S Inter-S routing between nd B B. Host h2 b B Intr-S routing within S B We ll exmine seifi inter-s nd intr-s Internet routing rotools shortly Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 Distributed Comuting Grou Comuter Networks R. Wttenhofer /32
The Internet Network Lyer IP ddressing: Introdution Host, router lyer funtions: Network lyer Routing rotools th seletion RIP, OSPF, BGP Trnsort lyer: TCP, UDP routing tble Link lyer hysil lyer IP rotool ddressing onventions dtgrm formt ket hndling onventions ICMP rotool error reorting router signling Distributed Comuting Grou Comuter Networks R. Wttenhofer /33 IP ddress: 32-bit identifier for host, router interfe Interfe: onnetion between host, router nd hysil link routers tyilly hve multile interfes host my hve multile interfes IP ddresses ssoited with interfe, not host or router 223... 223..2. 223...2 223... 223..2.9 223...3 223..3. 223..3.27 223..2.2 223..3.2 223... = 0 0000000 0000000 0000000 223 Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 IP ddressing IP ddressing IP ddress rt (high order bits) host rt (low order bits) Wht s (lol)? (from IP ddress ersetive) devie interfes with sme rt of IP ddress n hysilly reh eh other without intervening router 223... 223..2. 223...2 223... 223..2.9 223...3 223..3. 223..3.27 LN 223..2.2 223..3.2 onsisting of 3 IP s (for IP ddresses strting with 223, first 2 bits re ddress) How to find the s? Deth eh interfe from router or host rete islnds of isolted s Exmle on the right Interonneted system onsisting of six s 223..2. 223..9. 223... 223..2.6 223..9.2 223..8. 223..2.2 223...2 223...3 223..7.0 223..8.0 223..3. 223... 223..7. 223..3.27 223..3.2 Distributed Comuting Grou Comuter Networks R. Wttenhofer /35 Distributed Comuting Grou Comuter Networks R. Wttenhofer /36
IP ddresses IP ddressing: CIDR given notion of, let s re-exmine IP ddresses lss-full ddressing lss B C D 0 host 0 host 0 host 0 multist ddress 32 bits.0.0.0 to 27.255.255.255 28.0.0.0 to 9.255.255.255 92.0.0.0 to 223.255.255.255 22.0.0.0 to 239.255.255.255 lss-full ddressing: ineffiient use of ddress se, ddress se exhustion e.g., lss B net lloted enough ddresses for 65K hosts, even if only 2K hosts in tht CIDR: Clssless InterDomin Routing ortion of ddress of rbitrry length ddress formt:.b..d/x, where x is number of bits in ortion of ddress rt 00000 0000 0000000 00000000 200.23.6.0/23 host rt Distributed Comuting Grou Comuter Networks R. Wttenhofer /37 Distributed Comuting Grou Comuter Networks R. Wttenhofer /38 IP ddresses: how to get one? IP ddresses: how to get one? How do hosts get one? (host ortion) Either hrd-oded by system dmin in file Wintel: ontrol-nel onfigurtion t/i roerties UNIX: /et/r.onfig Or DHCP: Dynmi Host Configurtion Protool dynmilly get ddress: lug-nd-ly host brodsts DHCP disover messge DHCP server resonds with DHCP offer messge host requests IP ddress: DHCP request messge DHCP server sends ddress: DHCP k messge Network ( ortion) get lloted ortion of ISP s ddress se ISP's blok 00000 0000 0000000 00000000 200.23.6.0/20 Orgniztion 0 00000 0000 0000000 00000000 200.23.6.0/23 Orgniztion 00000 0000 000000 00000000 200.23.8.0/23 Orgniztion 2 00000 0000 000000 00000000 200.23.20.0/23....... Orgniztion 7 00000 0000 0000 00000000 200.23.30.0/23 Distributed Comuting Grou Comuter Networks R. Wttenhofer /39 Distributed Comuting Grou Comuter Networks R. Wttenhofer /0
Hierrhil ddressing: route ggregtion Hierrhil ddressing: more seifi routes Hierrhil ddressing llows effiient dvertisement of routing informtion: Wht if Orgniztion wnts to hnge the rovider? ISPs-R-Us hs more seifi route to Orgniztion Orgniztion 0 200.23.6.0/23 Orgniztion 200.23.8.0/23 Orgniztion 2 200.23.20.0/23 Orgniztion 7 200.23.30.0/23.... Fly-By-Night-ISP ISPs-R-Us Send me nything with ddresses beginning 200.23.6.0/20 Send me nything with ddresses beginning 99.3.0.0/6 Internet Orgniztion 0 200.23.6.0/23 Orgniztion 2 200.23.20.0/23 Orgniztion 7 200.23.30.0/23.... Orgniztion 200.23.8.0/23 Fly-By-Night-ISP ISPs-R-Us Send me nything with ddresses beginning 200.23.6.0/20 Send me nything with ddresses beginning 99.3.0.0/6 or 200.23.8.0/23 Internet Distributed Comuting Grou Comuter Networks R. Wttenhofer / Distributed Comuting Grou Comuter Networks R. Wttenhofer /2 IP ddressing: the lst word... Getting dtgrm from soure to destintion How does n ISP get blok of ddresses? from nother (bigger) ISP or with ICNN: Internet Corortion for ssigned Nmes nd Numbers llotes ddresses mnges DNS ssigns domin nmes, resolves disutes Will there be enough IP ddresses, ever? No, there re some hks round the orner (lter) Known s forwrding IP dtgrm: mis fields soure IP ddr dest IP ddr dt dtgrm remins unhnged, s it trvels from soure to destintion ddr fields of interest here B 223... 223..2. 223...2 223... 223..2.9 223...3 routing tble in Dest. Net. next router #hos 223.. 223..2 223... 2 223..3 223... 2 223..3.27 223..2.2 E 223..3. 223..3.2 Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 Distributed Comuting Grou Comuter Networks R. Wttenhofer /
Getting dtgrm from soure to destintion Getting dtgrm from soure to destintion mis fields 223... 223..2.2 dt Strting t, given IP dtgrm ddressed to B: look u net. ddress of B find B is on sme net. s link lyer will send dtgrm diretly to B inside link-lyer frme nd B re diretly onneted B Dest. Net. next router #hos 223.. 223..2 223... 2 223..3 223... 2 223... 223..2. 223...2 223... 223..2.9 223...3 223..3. 223..3.27 223..2.2 E 223..3.2 mis fields 223... 223..2.2 dt Strting t with destintion E look u ddress of E E on different, E not diretly tthed routing tble: next ho router to E is 223... link lyer sends dtgrm to router 223... inside linklyer frme dtgrm rrives t 223... B Dest. Net. next router #hos 223.. 223..2 223... 2 223..3 223... 2 223... 223..2. 223...2 223... 223..2.9 223...3 223..3. 223..3.27 223..2.2 E 223..3.2 Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 Distributed Comuting Grou Comuter Networks R. Wttenhofer /6 Getting dtgrm from soure to destintion IP dtgrm formt Dest. next mis fields 223... 223..2.2 dt router #hos interfe rriving t 223.., destined for 223..2.2 look u ddress of E E on sme s router s interfe 223..2.9 router, E diretly tthed link lyer sends dtgrm to 223..2.2 inside link-lyer frme vi interfe 223..2.9 dtgrm rrives t 223..2.2 (hoory!) 223.. - 223... 223..2-223..2.9 223..3-223..3.27 B 223... 223..2. 223...2 223... 223..2.9 223...3 223..3. 223..3.27 223..2.2 E 223..3.2 IP rotool version number heder length (bytes) tye of dt mx number remining hos (deremented t eh router) uer lyer rotool to deliver ylod to 32 bits ver hed. tye of len servie length frgment 6-bit identifier flgs offset time to uer Heder live lyer heksum 32 bit soure IP ddress 32 bit destintion IP ddress Otions (if ny) dt (vrible length, tyilly TCP or UDP segment) totl dtgrm length (bytes) for frgmenttion/ ressembly E.g. timestm, reord route tken, seify list of routers to visit. Distributed Comuting Grou Comuter Networks R. Wttenhofer /7 Distributed Comuting Grou Comuter Networks R. Wttenhofer /8
IP Frgmenttion nd Ressembly IP Frgmenttion nd Ressembly links hve MTU mx. trnsmission unit lrgest ossible linklevel frme lrge IP dtgrm divided ( frgmented ) within net one dtgrm beomes severl dtgrms ressembled only t finl destintion IP heder bits used to identify, order relted frgments ressembly frgmenttion: in: one lrge dtgrm out: 3 smller dtgrms length =000 ID =x frgflg =0 offset =0 One lrge dtgrm beomes severl smller dtgrms length =500 length =500 length =00 ID =x ID =x ID =x frgflg = frgflg = frgflg =0 offset =0 offset =80 offset =2960 Distributed Comuting Grou Comuter Networks R. Wttenhofer /9 Distributed Comuting Grou Comuter Networks R. Wttenhofer /50 ICMP: Internet Control Messge Protool DHCP: Dynmi Host Configurtion Protool used by hosts, routers, gtewys to ommunition -level informtion error reorting: unrehble host,, ort, rotool eho request/rely (used by ing) -lyer bove IP: ICMP msgs rried in IP dtgrms ICMP messge: tye, ode lus first 8 bytes of IP dtgrm using error Some tyil tyes/odes Tye Code desrition 0 0 eho rely (ing) 3 0 dest. unrehble 3 dest host unrehble 3 2 dest rotool unrehble 3 3 dest ort unrehble 3 6 dest unknown 3 7 dest host unknown 0 soure quenh (ongestion ontrol - not used) 8 0 eho request (ing) 9 0 route dvertisement 0 0 router disovery 0 TTL exired 2 0 bd IP heder Gols llow host to dynmilly obtin its IP ddress from server when it joins Cn renew its lese on ddress in use llows reuse of ddresses (only hold ddress while onneted nd on ) Suort for mobile users who wnt to join (more shortly) DHCP review host brodsts DHCP disover messge DHCP server resonds with DHCP offer messge host requests IP ddress: DHCP request messge DHCP server sends ddress: DHCP k messge Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 Distributed Comuting Grou Comuter Networks R. Wttenhofer /52
DHCP lient-server senrio DHCP lient-server senrio B 223... 223...2 223... 223..2.9 223...3 223..3. DHCP server 223..3.27 223..2.2 E 223..3.2 223..2. rriving DHCP lient needs ddress in this DHCP server: 223..2.5 time DHCP disover sr : 0.0.0.0, 68 dest.: 255.255.255.255,67 yiddr: 0.0.0.0 trnstion ID: 65 DHCP offer sr: 223..2.5, 67 dest: 255.255.255.255, 68 yiddrr: 223..2. trnstion ID: 65 Lifetime: 3600 ses DHCP request sr: 0.0.0.0, 68 dest:: 255.255.255.255, 67 yiddrr: 223..2. trnstion ID: 655 Lifetime: 3600 ses rriving lient DHCP CK sr: 223..2.5, 67 dest: 255.255.255.255, 68 yiddrr: 223..2. trnstion ID: 655 Lifetime: 3600 ses Distributed Comuting Grou Comuter Networks R. Wttenhofer /53 Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 NT: Network ddress Trnsltion NT: Network ddress Trnsltion rest of Internet 38.76.29.7 ll dtgrms leving lol hve sme single soure NT IP ddress: 38.76.29.7, different soure ort numbers 0.0.0. lol (e.g., home ) 0.0.0/2 Dtgrms with soure or destintion in this hve 0.0.0/2 ddress for soure, destintion (s usul) 0.0.0. 0.0.0.2 0.0.0.3 Motivtion lol uses just one IP ddress s fr s outside world is onerned no need to be lloted rnge of ddresses from ISP just one IP ddress is used for ll devies n hnge ddresses of devies in lol without notifying outside world n hnge ISP without hnging ddresses of devies in lol devies inside lol net not exliitly ddressble, visible by outside world ( seurity lus). BUT: mhines nnot be servers! Distributed Comuting Grou Comuter Networks R. Wttenhofer /55 Distributed Comuting Grou Comuter Networks R. Wttenhofer /56
NT: Network ddress Trnsltion NT: Network ddress Trnsltion Imlementtion: NT router must outgoing dtgrms: rele (soure IP ddress, ort #) of every outgoing dtgrm to (NT IP ddress, new ort #) remote lients/servers will resond using (NT IP ddress, new ort #) s destintion ddr. remember (in NT trnsltion tble) every (soure IP ddress, ort #) to (NT IP ddress, new ort #) trnsltion ir inoming dtgrms: rele (NT IP ddress, new ort #) in dest fields of every inoming dtgrm with orresonding (soure IP ddress, ort #) stored in NT tble 2: NT router hnges dtgrm soure ddr from 0.0.0., 335 to 38.76.29.7, 500, udtes tble 2 NT trnsltion tble WN side ddr LN side ddr 38.76.29.7, 500 0.0.0., 335 S: 38.76.29.7, 500 D: 28.9.0.86, 80 38.76.29.7 S: 28.9.0.86, 80 D: 38.76.29.7, 500 3 3: Rely rrives dest. ddress: 38.76.29.7, 500 0.0.0. S: 0.0.0., 335 D: 28.9.0.86, 80 S: 28.9.0.86, 80 D: 0.0.0., 335 : host 0.0.0. sends dtgrm to 28.9.0, 80 0.0.0. 0.0.0.2 0.0.0.3 : NT router hnges dtgrm dest ddr from 38.76.29.7, 500 to 0.0.0., 335 Distributed Comuting Grou Comuter Networks R. Wttenhofer /57 Distributed Comuting Grou Comuter Networks R. Wttenhofer /58 NT: Network ddress Trnsltion Routing in the Internet 6-bit ort-number field 60,000 simultneous onnetions with single LN-side ddress! NT is ontroversil routers should only roess u to lyer 3 violtes end-to-end rgument NT ossibility must be tken into ount by designers, e.g., P2P litions ddress shortge should insted be solved by IPv6 delys deloyment of IPv6 The Globl Internet onsists of utonomous Systems (S) interonneted with eh other. There re severl tyes Stub S: smll orortion Multihomed S: lrge orortion (no trnsit) Trnsit S: rovider Two-level routing Intr-S: dministrtor is resonsible for hoie Inter-S: unique stndrd Distributed Comuting Grou Comuter Networks R. Wttenhofer /59 Distributed Comuting Grou Comuter Networks R. Wttenhofer /60
Internet S Hierrhy Intr-S Routing Intr-S border (exterior gtewy) routers lso known s Interior Gtewy Protools (IGP) Most ommon IGPs: RIP: Routing Informtion Protool OSPF: Oen Shortest Pth First IGRP: Interior Gtewy Routing Protool (Ciso rorietry) Inter-S interior (gtewy) routers Distributed Comuting Grou Comuter Networks R. Wttenhofer /6 Distributed Comuting Grou Comuter Networks R. Wttenhofer /62 RIP (Routing Informtion Protool) RIP (Routing Informtion Protool) Distne vetor lgorithm Inluded in BSD-UNIX Distribution in 982 Distne metri: number of hos (mx = 5 hos) Cn you guess why? Distne vetors: exhnged every 30 se vi Resonse Messge (lso lled dvertisement ) Eh dvertisement: route to u to 25 destintion s within S w x y D B C Destintion Network Next Router Num. of hos to dest. w 2 y B 2 z B 7 x --..... Routing tble in D z Distributed Comuting Grou Comuter Networks R. Wttenhofer /63 Distributed Comuting Grou Comuter Networks R. Wttenhofer /6
RIP: Link Filure nd Reovery Distne Vetor: oisoned reverse If no dvertisement herd fter 80 se neighbor/link delred ded routes vi neighbor invlidted new dvertisements sent to neighbors neighbors in turn send out new dvertisements (if tbles hnged) link filure info quikly rogtes to entire net oison reverse (next slide) used to revent ing-ong loos (infinite distne = 6 hos) If Z routes through Y to get to X : Z tells Y its (Z s) distne to X is infinite (so Y won t route to X vi Z) will this omletely solve ount to infinity roblem? 60 X Y 50 Z lgorithm termintes Distributed Comuting Grou Comuter Networks R. Wttenhofer /65 Distributed Comuting Grou Comuter Networks R. Wttenhofer /66 RIP Tble roessing RIP Tble exmle (ontinued) RIP routing tbles mnged by lition-level roess lled route-d (demon) dvertisements sent in UDP kets, eriodilly reeted Router: giroflee.euroom.fr Destintion Gtewy Flgs Ref Use Interfe -------------------- -------------------- ----- ----- ------ --------- 27.0.0. 27.0.0. UH 0 2692 lo0 92.68.2. 92.68.2.5 U 2 3 f0 93.55.. 93.55..6 U 3 58503 le0 92.68.3. 92.68.3.5 U 2 25 q0 22.0.0.0 93.55..6 U 3 0 le0 defult 93.55..29 UG 0 35 Three tthed lss C s (LNs) Router only knows routes to tthed LNs Defult router used to go u Route multist ddress: 22.0.0.0 Loobk interfe (for debugging) Distributed Comuting Grou Comuter Networks R. Wttenhofer /67 Distributed Comuting Grou Comuter Networks R. Wttenhofer /68
OSPF (Oen Shortest Pth First) OSPF dvned fetures (not in RIP) oen : ublily vilble Uses Link Stte lgorithm LS ket dissemintion Toology m t eh node Route omuttion using Dijkstr s lgorithm OSPF dvertisement rries one entry er neighbor router dvertisements disseminted to entire S (vi flooding) Seurity ll OSPF messges uthentited therefore no mliious intrusion TCP onnetions used Multile sme-ost ths llowed (only one th in RIP) For eh link, multile ost metris for different TOS e.g., stellite link ost set low for best effort; high for rel time Integrted uni- nd multist suort: Multist OSPF (MOSPF) uses sme toology dt bse s OSPF Hierrhil OSPF in lrge domins Distributed Comuting Grou Comuter Networks R. Wttenhofer /69 Distributed Comuting Grou Comuter Networks R. Wttenhofer /70 Hierrhil OSPF Hierrhil OSPF Two-level hierrhy: lol re or bkbone Link-stte dvertisements only in re eh node hs detiled re toology but only knows diretion (shortest th) to nets in other res. re border routers summrize distnes to s in own re dvertise to other re border routers. Bkbone routers run OSPF routing limited to bkbone. Boundry routers onnet to other Ss. Distributed Comuting Grou Comuter Networks R. Wttenhofer /7 Distributed Comuting Grou Comuter Networks R. Wttenhofer /72
[E]IGRP: [Enhned] Interior Gtewy Routing Protool Inter-S routing CISCO rorietry; suessor of RIP (mid 80s) Distne Vetor, like RIP severl ost metris (dely, bndwidth, relibility, lod et) uses TCP to exhnge routing udtes Loo-free routing vi Distributed Udting lgorithm (DUL) bsed on diffused omuttion Distributed Comuting Grou Comuter Networks R. Wttenhofer /73 Distributed Comuting Grou Comuter Networks R. Wttenhofer /7 Remember: Count to Infinity Problem BGP does not ount to infinity : 2 : b b d e : : 6 : 8 : 7 : 5 : 3 Destintion Destintion Dir Dir Dst Pth b 5 bdez Dst Pth dez Distributed Comuting Grou Comuter Networks R. Wttenhofer /75 Distributed Comuting Grou Comuter Networks R. Wttenhofer /76
BGP does not ount to infinity BGP Bsis Continued withdrw nnoune bdez b d e b d e Destintion Dir Dst Pth Destintion Dir Dst Pth dez dez Destintion Dir Dst Pth Destintion Dir Dst Pth b 5 bdez b 5 bdez Distributed Comuting Grou Comuter Networks R. Wttenhofer /77 Distributed Comuting Grou Comuter Networks R. Wttenhofer /78 BGP Bsis Continued BGP Bsis Continued nnoune bfez 30s b d e f nnoune bdez b d e f Destintion Dir Dst Pth Destintion Dir Dst Pth f 3 dez fez bku tive f 3 dez fez bku tive Destintion Dir Dst Pth Destintion Dir Dst Pth b bfez b bfez Distributed Comuting Grou Comuter Networks R. Wttenhofer /79 Distributed Comuting Grou Comuter Networks R. Wttenhofer /80
BGP (Border Gtewy Protool) Internet rhiteture BGP is the Internet de-fto stndrd Pth Vetor rotool Destintion Dir Dst Pth dez ) Reeive BGP udte (nnoune or withdrwl) from neighbor. 2) Udte routing tble. 3) Does udte ffet tive route? (Loo detetion, oliy, et.) If yes, send udte to ll neighbors tht re llowed by oliy. MinRoutedver: t most nnoune er neighbor er 30+jitter seonds. Store the tive routes of the neighbors. 72.30.60/9 R ibgp Route fl dmening Multith Soft onfigurtion 239 356 BGP BGP BGP Distributed Comuting Grou Comuter Networks R. Wttenhofer /8 Distributed Comuting Grou Comuter Networks R. Wttenhofer /82 Internet inter-s routing: BGP Robustness of BGP BGP messges exhnged using TCP. BGP messges OPEN: oens TCP onnetion to eer nd uthentites sender UPDTE: dvertises new th (or withdrws old) KEEPLIVE kees onnetion live in bsene of UPDTES; lso CKs OPEN request NOTIFICTION: reorts errors in revious msg; lso used to lose onnetion Poliy Even if two BGP routers re onneted they my not nnoune ll their routes or use ll the routes of the other Exmle: if S does not wnt to route trffi of S B, then should simly not nnoune nything to B. b d We re interested in routes to destintion d. Nodes,b, ll hve the oliy to refer 2-ho route through their lokwise neighbor over diret -ho route to destintion d. Distributed Comuting Grou Comuter Networks R. Wttenhofer /83 Distributed Comuting Grou Comuter Networks R. Wttenhofer /8
BGP Udte Trffi (Me-Est) Internet Evolution: NSFNet (995) 2,000,000,800,000,600,000,00,000,200,000,000,000 800,000 600,000 00,000 200,000 0 /7/997 7/7/997 0/7/997 /7/998 /7/998 nnounements Withdrws 7/7/998 Ciso bug withdrw loo is fixed with IOS relese. 0/7/998 /7/999 /7/999 7/7/999 0/7/999 /7/2000 NSFNet Bkbone Hello/EGP Hello/EGP Regionl Regionl Regionl Cmus Cmus Cmus Cmus Distributed Comuting Grou Comuter Networks R. Wttenhofer /85 Distributed Comuting Grou Comuter Networks R. Wttenhofer /86 Internet Evolution: Tody Exerimentl Setu S S2 BGP S5 S6 S3 S7 S S8 nlyzed seondry ths of 20x20 S irs: Injet nd monitor BGP fults. Survey roviders on oliies. Distributed Comuting Grou Comuter Networks R. Wttenhofer /87 Distributed Comuting Grou Comuter Networks R. Wttenhofer /88
BGP Convergene Times BGP Convergene Results Cumultive Perentge 00 80 60 0 20 0 0 20 0 60 80 00 20 0 60 80 If link omes u, the onvergene time is in the order of time to forwrd messge on the shortest th. If link goes down, the onvergene time is in the order of time to forwrd messge on the longest th. Seonds Until Convergene New Link New Route Filure, Bku exists New Link Better Route Filure, No Bku Distributed Comuting Grou Comuter Networks R. Wttenhofer /89 Distributed Comuting Grou Comuter Networks R. Wttenhofer /90 Intuition for Slow Convergene Intuition for Slow Convergene Os O.2s 30s!!! : : - - b d e f b d e f b d ed b W d e f db ed b W d e f b: : d: e: b: : d: e: - b: : d: e: :b d: e:d - - :b d: e:d O.s 60s 90s : : - - W W W W W b d e f b d ed b W d e f edb b d W e f b d e W f b: : d: e: b: : d: e: - - - d:b e:d - - - - e:db Distributed Comuting Grou Comuter Networks R. Wttenhofer /9 Distributed Comuting Grou Comuter Networks R. Wttenhofer /92
Intuition for Slow Convergene Exmle of BGP Convergene Time BGP Messge/Event b d e f 0:0:30 229 withdrws 0::08 27 nnounes 5696 229 0::32 27 nnounes 5696 229 0::50 27 nnounes 20 3508 3508 50 7037 239 5696 229 0:2:7 27 nnounes 20 3508 3508 50 7037 239 5696 229 0:3:05 27 nnounes 20 3508 3508 50 7037 239 63 5696 229 0:3:35 27 nnounes 20 3508 3508 50 7037 239 63 5696 229 0:3:59 27 withdrws Convergene in the time to forwrd messge on the longest th. Distributed Comuting Grou Comuter Networks R. Wttenhofer /93 Distributed Comuting Grou Comuter Networks R. Wttenhofer /9 Remember the Exmle Wht might hel? Ide: tth use tg to the withdrwl messge identifying the filed link/node (for given refix). W It n be shown tht use tg redues the onvergene time to the shortest th b d e f ed Problems Sine BGP is widely deloyed, it nnot be hnged esily ISP s (S s) don t like the world to know tht it is their link tht is not stble, nd use tgs do extly tht. Re onditions mke the use tgs rotool intrite ed edb Distributed Comuting Grou Comuter Networks R. Wttenhofer W /95 Distributed Comuting Grou Comuter Networks R. Wttenhofer /96
Exmle with BGP-CT (Cuse Tgs) Exmle with BGP-CT Os : : b d e f b d e f b: : d: e: b: : d: e: Distributed Comuting Grou Comuter Networks R. Wttenhofer /97 Distributed Comuting Grou Comuter Networks R. Wttenhofer /98 Exmle with BGP-CT Convergene Time using Cuse Tgs O.s : b x W() W() W() W() W() b d e f e f b: : d: e: Distributed Comuting Grou Comuter Networks R. Wttenhofer /99 Distributed Comuting Grou Comuter Networks R. Wttenhofer /00
Convergene Time using Cuse Tgs Convergene Time using Cuse Tgs b b x x e f e f Convergene in the time to forwrd messge on the new shortest th (insted of the longest). Distributed Comuting Grou Comuter Networks R. Wttenhofer /0 Distributed Comuting Grou Comuter Networks R. Wttenhofer /02 Why re Intr- nd Inter-S routing different? Router rhiteture Overview Poliy Inter-S: dmin wnts ontrol over how its trffi routed, nd who routes through its net. Intr-S: single dmin, so no oliy deisions needed Sle hierrhil routing sves tble size, redued udte trffi Performne Intr-S: n fous on erformne Inter-S: oliy my dominte over erformne Two key router funtions run routing lgorithms/rotools (RIP, OSPF, BGP) swith dtgrms from inoming to outgoing link Distributed Comuting Grou Comuter Networks R. Wttenhofer /03 Distributed Comuting Grou Comuter Networks R. Wttenhofer /0
Inut Port Funtions Inut Port Queuing Physil lyer bit-level reetion Dt link lyer e.g., Ethernet see hter 5 Deentrlized swithing given dtgrm dest., looku outut ort using routing tble in inut ort memory gol: omlete inut ort roessing t line seed queuing: if dtgrms rrive fster thn forwrding rte into swith fbri Fbri slower tht inut orts ombined queueing my our t inut queues Hed-of-the-Line (HOL) bloking queued dtgrm t front of queue revents others in queue from moving forwrd queuing dely nd loss due to inut buffer overflow Distributed Comuting Grou Comuter Networks R. Wttenhofer /05 Distributed Comuting Grou Comuter Networks R. Wttenhofer /06 Three tyes of swithing fbris Swithing Vi Memory First genertion routers ket oied by system s (single) CPU seed limited by memory bndwidth (2 bus rossings er dtgrm) Inut Port Memory Outut Port System Bus Modern routers inut ort roessor erforms looku, oy into memory Ciso Ctlyst 8500 Distributed Comuting Grou Comuter Networks R. Wttenhofer /07 Distributed Comuting Grou Comuter Networks R. Wttenhofer /08
Swithing Vi Bus or Interonnetion Network Outut orts dtgrm from inut ort memory to outut ort memory vi shred bus bus ontention: swithing seed limited by bus bndwidth Gbs bus, Ciso 900: suffiient seed for ess nd enterrise routers (not regionl or bkbone) Interonnetion Network: overome bus bndwidth limittions Bnyn s, other interonnetion nets initilly develoed to onnet roessors in multiroessor dvned design: frgmenting dtgrm into fixed length ells, swith ells through the fbri. Ciso 2000: swithes Gbs through the interonnetion Buffering required when dtgrms rrive from fbri fster thn the trnsmission rte Sheduling disiline hooses mong queued dtgrms for trnsmission Distributed Comuting Grou Comuter Networks R. Wttenhofer /09 Distributed Comuting Grou Comuter Networks R. Wttenhofer /0 Outut ort queuing IPv6 buffering when rrivl rte vi swith exeeds outut line seed queuing (dely) nd loss due to outut ort buffer overflow Initil motivtion: 32-bit ddress se omletely lloted by 2008. dditionl motivtion heder formt hels seed roessing/forwrding heder hnges to filitte QoS (qulity of servie) new nyst ddress: route to best of severl relited servers IPv6 dtgrm formt: fixed-length 0 byte heder no frgmenttion llowed Distributed Comuting Grou Comuter Networks R. Wttenhofer / Distributed Comuting Grou Comuter Networks R. Wttenhofer /2
IPv6 Heder Other Chnges from IPv Priority identify riority mong dtgrms in flow Flow Lbel identify dtgrms in sme flow (onet of flow not well defined) Next heder identify uer lyer rotool for dt Cheksum removed entirely to redue roessing time t eh ho Otions llowed, but outside of heder indited by Next Heder field ICMPv6: new version of ICMP dditionl messge tyes, e.g. Pket Too Big multist grou mngement funtions Distributed Comuting Grou Comuter Networks R. Wttenhofer /3 Distributed Comuting Grou Comuter Networks R. Wttenhofer / Trnsition From IPv To IPv6 Dul Stk roh Not ll routers n be ugrded simultneously no flg dys How will the oerte with mixed IPv nd IPv6 routers? Two roosed rohes Dul Stk some routers with dul stk (v6, v) n trnslte between formts Tunneling IPv6 rried s ylod in IPv dtgrm mong IPv routers Distributed Comuting Grou Comuter Networks R. Wttenhofer /5 Distributed Comuting Grou Comuter Networks R. Wttenhofer /6
Tunneling IPv6 inside IPv where needed Distributed Comuting Grou Comuter Networks R. Wttenhofer /7