Routing: Network Lyer Prt II Routing & orwrding: Logicl View of Router Routing lgorithms: Link stte vs. istnce Vector Routing in the Internet Intr-S vs. Inter-S routing Intr-S: RIP nd OSP Inter-S: GP nd Policy Routing MPLS Redings: Textbook: hpter : Sections.-.,.-.6 sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II. Remove pcket from n input queue IP orwrding Process. heck for snity, decrement TTL field. Plce pcket on correct output queue IP orwrding Tble estintion Next Hop Interfce If queues get full, just drop pckets! orwrding Process. Mtch pcket s destintion to tble entry IP orwrding Tble If queues get full, just drop pckets! Router Net Net Net, Host Router irect Router INT 7 INT INT Net Router INT 7 destintion is usully network. My lso be host, or gtewy of lst resort (defult) The next hop is either directly connected network or router on directly connected network physicl interfce sci omputer Networks sci omputer Networks How re orwrding Tbles Populted to Implement Routing? Stticlly dministrtor mnully configures forwrding tble entries + More control + Not restricted to destintion-bsed forwrding - oesn t scle - Slow to dpt to network filures ynmiclly Routers exchnge network rechbility informtion using ROUTING PROTOOLS. Routers use this to compute best routes + n rpidly dpt to chnges in network topology + n be mde to scle well - omplex distributed lgorithms - onsume PU, ndwidth, Memory - ebugging cn be difficult - urrent protocols re destintion-bsed In prctice : mix of these. Sttic routing mostly t the edge sci omputer Networks S ynmic Routing: Intr- vs. Inter-S OSP IGP = Interior Gtewy Protocol Metric bsed: OSP, IS-IS, RIP, IGRP (cisco) GP = xterior Gtewy Protocol S GP Policy bsed: GP The Routing omin of GP is the entire Internet IGRP sci omputer Networks Routing nd Network Lyer Prt II 6
Internet S Hierrchy Intr-S vs. Inter-S Routing border (exterior gtewy) routers Host h.b b. Inter-S routing between nd.c d b c Intr-S routing within S. c b Host h Intr-S routing within S interior routers sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 8 Intr-S nd Inter-S Routing.b b d. b inter-s, intr-s routing in gtewy.c.c c. c Gtewys : perform inter- S routing mongst b themselves perform intr- S routing with other routers in their S network lyer link lyer physicl lyer Where oes orwrding Tble ome rom? RIP omin GP OSP omin RIP Process RIP Routing tbles OSP Process OSP Routing tbles GP Process GP Routing tbles orwrding Tble Mnger orwrding Tble sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing sic Routing Problem Gol: determine good pth through the network from source to destintion Good mens usully the shortest pth Network modeled s grph Routers nodes Link edges dge cost: dely, congestion level, ssume network with N nodes, where ech edge is ssocited cost node knows only its neighbors nd the cost to rech them How does ech node lern how to rech every other node long the shortest pth? sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II
Routing: Issues How re routing tbles determined? Who determines tble entries? Wht info is used in determining tble entries? When do routing tble entries chnge? Where is routing info stored? How to control routing tble size? nswer these questions, we re done! Routing Prdigms Hop-by-hop Routing ch pcket contins destintion ddress ch router chooses next-hop to destintion routing decision mde t ech (intermedite) hop! pckets to sme destintion my tke different pths! xmple: IP s defult dtgrm routing Source Routing Sender selects the pth to destintion precisely Routers forwrd pcket to next-hop s specified Problem: if specified pth no longer vlid due to link filure! xmple: IP s loose/strict source route option virtul circuit setup phse in TM (or MPLS) sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II Routing lgorithms/protocols Issues Need to e ddressed: Route selection my depend on different criteri Performnce: choose route with the smllest dely Policy: choose route tht doesn t cross.gov network dpt to chnges in network topology or condition Self-heling: little or no humn intervention Sclbility Must be ble to support lrge number of hosts, routers entrlized vs. istributed Routing lgorithms entrlized: centrlized route server collects routing informtion nd network topology, mkes route selection decisions, then distributes them to routers istributed: Routers cooperte using distributed protocol to crete mutully consistent routing tbles Two stndrd distributed routing lgorithms Link Stte (LS) routing istnce Vector (V) routing sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 6 Link Stte vs istnce Vector oth ssume tht The ddress of ech neighbor is known The cost of reching ech neighbor is known oth find globl informtion g y exchnging routing info mong neighbors iffer in the informtion exchnged nd route computtion LS: tells every other node its distnces to neighbors V: tells neighbors its distnce to every other node sci omputer Networks Routing nd Network Lyer Prt II 7 Link Stte lgorithm sic ide: istribute link stte pcket to ll routers Topology of the network ost of ech link in the network ch router independently computes optiml pths rom itself to every destintion Routes re gurnteed to be loop free if ch router sees the sme cost for ech link Uses the sme lgorithm to compute the best pth sci omputer Networks Routing nd Network Lyer Prt II 8
Link Stte: ontrol Trffic ch node floods its locl informtion to every other node in the network ch node ends up knowing the entire network topology use ijkstr to compute the shortest pth to every other node Host Host N N Host N N N6 N7 N Host Host Host Host Link Stte: Node Stte Host Host N N N N N Host N6 N7 sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing nd Network Lyer Prt II Topology issemintion Topology tbse: xmple ch router cretes set of link stte pckets (LSPs) escribing its links to neighbors LSP contins Router id, neighbor s id, nd cost to its neighbor opies of LSPs re distributed to ll routers Using controlled flooding ch router mintins topology dtbse tbse contining ll LSPs link stte dtbse sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II onstructing Routing Tble: ijkstr s lgorithm Given the network topology How to compute the shortest pth to ech destintion? Some nottion : source node N: set of nodes to which shortest pths re known so fr N is initilly empty (V): the cost of the known shortest pth from source to V (U,V): cost of link U to V (U,V) = if not neighbors lgorithm (t Node ) Initiliztion N = {} or ll nodes V If V djcent to, (V) = (,V) else (V) = Loop ind U not in N such tht (U) is the smllest dd U into set N Updte (V) for ll V not in N (V) = min{(v), (U) + (U,V)} Until ll nodes in N sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II
Step xmple: ijkstr s lgorithm strt N (),p() (),p() (),p(),,, (),p() (),p() Initiliztion: N = {}; for ll nodes v if v djcent to then (v) = c(,v); 6 else (v) = ; Step xmple: ijkstr s lgorithm strt N (),p() (),p() (),p(),,,, (),p(), (),p() 8 Loop 9 find w not in N s.t. (w) is minimum; dd w to N; updte (v) for ll v djcent to w nd not in N: (v) = min( (v), (w) + c(w,v) ); until ll nodes in N; sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 6 Step xmple: ijkstr s lgorithm strt N (),p(), (),p(),,, (),p(), (),p(), (),p(), 8 Loop 9 find w not in N s.t. (w) is minimum; dd w to N; updte (v) for ll v djcent to w nd not in N: (v) = min( (v), (w) + c(w,v) ); until ll nodes in N; Step xmple: ijkstr s lgorithm strt N (),p(), (),p(),,, (),p(), (),p(), (),p(), 8 Loop 9 find w not in N s.t. (w) is minimum; dd w to N; updte (v) for ll v djcent to w nd not in N: (v) = min( (v), (w) + c(w,v) ); until ll nodes in N; sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 8 Step xmple: ijkstr s lgorithm strt N (),p(), (),p(),,, (),p(), (),p(), (),p(), 8 Loop 9 find w not in N s.t. (w) is minimum; dd w to N; updte (v) for ll v djcent to w nd not in N: (v) = min( (v), (w) + c(w,v) ); until ll nodes in N; Step xmple: ijkstr s lgorithm strt N (),p(), (),p(),,, (),p(), (),p(), (),p(), 8 Loop 9 find w not in N s.t. (w) is minimum; dd w to N; updte (v) for ll v djcent to w nd not in N: (v) = min( (v), (w) + c(w,v) ); until ll nodes in N; sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing nd Network Lyer Prt II
Step ijkstr s lgorithm: In Nutshell strt N (),p(),,, (),p() (),p(),,,,, (),p() infinity, (),p() infinity infinity,,, Routing Tble omputtion dest next sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II istnce Vector Routing router tells neighbors its distnce to every router ommuniction between neighbors only sed on ellmn-ord lgorithm omputes shortest pths ch router mintins distnce tble row for ech possible destintion column for ech neighbor (Y,Z) : distnce from to Y vi Z xchnges distnce vector (the tble) with neighbors istnce vector: current lest cost to ech destintion istnce Vector: ontrol Trffic When the routing tble of node chnges, the node sends its tble to its neighbors node updtes its tble with informtion received from its neighbors Host Host N N Host N N N6 N7 N Host Host sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II istnce Tble: xmple istnce Tble to Routing Tble 6 8 () cost to destintion vi 7 8 8 9 cost to destintion vi () 7 8 6 9 Outgoing link to use, cost,,,, istnce tble Routing tble sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 6 6
istnce Vector Routing lgorithm istnce Vector Routing: Overview itertive: continues until no nodes exchnge info. self-terminting: no signl to stop synchronous: nodes need not exchnge info/iterte in lock step! distributed: ech node tlks only with directly-ttched neighbors istnce Tble dt structure ech node hs its own row for ech possible destintion column for ech directly-ttched neighbor to node exmple: in node, for dest. Y vi neighbor Z: (Y,Z) = = distnce from to Y, vi Z s next hop Z c(,z) + min { (Y,w)} w Itertive, synchronous: ech itertion cused by: locl link cost chnge messge from neighbor: its lest cost pth chnge from neighbor istributed: ech node notifies neighbors only when its lest cost pth to ny destintion chnges neighbors then notify their neighbors if necessry ch node: wit for (chnge in locl link cost or msg from neighbor) recompute distnce tble if lest cost pth to ny dest hs chnged, notify neighbors sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 8 istnce Vector lgorithm: xmple istnce Vector lgorithm: xmple Y 7 Z Z (Y,Z) = c(,z) + min { (Y,w)} w = 7+ = 8 Y 7 Z Y (Z,Y) = c(,y) + min { (Z,w)} w = + = sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing nd Network Lyer Prt II onvergence of V Routing Problems with V Routing router detects locl link cost chnge updtes distnce tble if cost chnge in lest cost pth, notify neighbors Y Z Link cost chnges: good news trvels fst bd news trvels slow count to infinity problem! 6 Y Z good news trvels fst lgorithm termintes lgorithm continues on! sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 7
ount-to-infinity Problem Y Z ixes to ount-to-infinity Problem Split horizon router never dvertises the cost of destintion to neighbor If this neighbor is the next hop to tht destintion Split horizon with poisonous reverse If routes trffic to Z vi Y, then tells Y tht its distnce to Z is infinity Insted of not telling nything t ll ccelertes convergence sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II Split Horizon with Poisoned Reverse If Z routes through Y to get to : Z tells Y its (Z s) distnce to is infinite (so Y won t route to vi Z) 6 Y Z lgorithm termintes ount-to-infinity Problem Revisited Y Z W sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 6 Link Stte vs istnce Vector Tells everyone bout neighbors ontrolled flooding to exchnge link stte ijkstr s s lgorithm ch router computes its own tble My hve oscilltions Open Shortest Pth irst (OSP) Tells neighbors bout everyone xchnges distnce vectors with neighbors ellmn-ord lgorithm ch router s tble is used by others My hve routing loops Routing Informtion Protocol (RIP) Link Stte vs. istnce Vector (cont d) Messge complexity LS: O(n *e) messges n: number of nodes e: number of edges V: O(d*n*k) messges d: node s degree k: number of rounds Time complexity LS: O(n*log n) V: O(n) onvergence time LS: O() V: O(k) Robustness: wht hppens if router mlfunctions? LS: node cn dvertise incorrect link cost ech node computes only its own tble V: node cn dvertise incorrect pth cost ech node s tble used by others; error propgte through network sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 8 8
Routing in the Rel World Our routing study thus fr - ideliztion ll routers identicl network flt How to do routing in the Internet sclbility nd policy issues scle: with million destintions: cn t store ll dest s in routing tbles! routing tble exchnge would swmp links! dministrtive i ti utonomy internet = network of networks ech network dmin my wnt to control routing in its own network Routing in the Internet The Globl Internet consists of utonomous Systems (S) interconnected with ech other hierrchiclly: Stub S: smll corportion: one connection to other S s Multihomed S: lrge corportion (no trnsit): multiple connections to other S s Trnsit S: provider, hooking mny S s together Two-level routing: Intr-S: dministrtor responsible for choice of routing lgorithm within network Inter-S: unique stndrd for inter-s routing: GP sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing nd Network Lyer Prt II Internet rchitecture Internet: networks of networks! Internet S Hierrchy Inter-S border (exterior gtewy) routers NP Internic Interntionl lines ntionl network regionl network on-line services ISP compny LNs university compny ISP ccess vi modem Intr-S interior (gtewy) routers sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II Intr-S vs. Inter-S Routing Why ifferent Intr- nd Inter-S Routing? Inter-S.b routing between. nd b.c Host d h c b Intr-S routing within S. c b Host h Intr-S routing within S Policy: Inter-S: dmin wnts control over how its trffic routed, who routes through its net. Intr-S: single dmin, so no policy decisions needed Scle: hierrchicl routing sves tble size, updte trffic Performnce: Intr-S: cn focus on performnce Inter-S: policy my dominte over performnce sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 9
Intr-S nd Inter-S Routing.b b d. b inter-s, intr-s routing in gtewy.c.c c. c Gtewys : perform inter- S routing mongst b themselves perform intr- S routers with other routers in their S network lyer link lyer physicl lyer Intr-S Routing lso known s Interior Gtewy Protocols (IGP) Most common Intr-S routing protocols: RIP: Routing Informtion Protocol OSP: Open Shortest Pth irst IS-IS: Intermedite System to Intermedite System (OSI Stndrd) IGRP: xtended Interior Gtewy Routing Protocol (isco proprietry) sci omputer Networks Routing nd Network Lyer Prt II sci omputer Networks Routing nd Network Lyer Prt II 6 RIP ( Routing Informtion Protocol) istnce vector lgorithm Included in S-UNI istribution in 98 istnce metric: # of hops (mx = hops) Number of hops from source router to vrious subnets: z u v w x y destintion hops u v w x y z sci omputer Networks Routing nd Network Lyer Prt II 7 RIP dvertisements istnce vectors: exchnged mong neighbors every sec vi Response Messge (lso clled dvertisement) ch dvertisement: list of up to destintion nets within S sci omputer Networks Routing nd Network Lyer Prt II 8 RIP: xmple w x y estintion Network Next Router Num. of hops to dest. w y z 7 x --..... Routing tble in sci omputer Networks Routing nd Network Lyer Prt II 9 z est Next hops w - - x - - z.... RIP: xmple dvertisement from to w x y estintion Network Next Router Num. of hops to dest. w y z 7 x --..... sci omputer Networks Routing nd Network Lyer Prt II Routing tble in 6 z
RIP: Link ilure nd Recovery If no dvertisement herd fter 8 sec --> neighbor/link declred ded routes vi neighbor invlidted new dvertisements sent to neighbors neighbors in turn send out new dvertisements (if tbles chnged) link filure info quickly propgtes to entire net poison reverse used to prevent ping-pong loops (infinite distnce = 6 hops) sci omputer Networks Routing nd Network Lyer Prt II 6 RIP Tble processing RIP routing tbles mnged by ppliction-level process clled route-d (demon) dvertisements sent in UP pckets, periodiclly repeted routed routed Trnsprt (UP) network (IP) link physicl forwrding tble forwrding tble Trnsprt (UP) network (IP) link physicl sci omputer Networks Routing nd Network Lyer Prt II 6 OSP (Open Shortest Pth irst) open : publicly vilble Uses Link Stte lgorithm LS pcket dissemintion Topology mp t ech node Route computtion using ijkstr s lgorithm OSP dvertisement crries one entry per neighbor router dvertisements disseminted to entire S (vi flooding) rried in OSP messges directly over IP (rther thn TP or UP OSP dvnced fetures (not in RIP) Security: ll OSP messges uthenticted (to prevent mlicious intrusion) Multiple sme-cost pths llowed (only one pth in RIP) or ech link, multiple l cost metrics for different TOS (e.g., stellite link cost set low for best effort; high for rel time) Integrted uni- nd multicst support: Multicst OSP (MOSP) uses sme topology dt bse s OSP Hierrchicl OSP in lrge domins. sci omputer Networks Routing nd Network Lyer Prt II 6 sci omputer Networks Routing nd Network Lyer Prt II 6 Hierrchicl OSP Hierrchicl OSP Two-level hierrchy: locl re, bckbone. Link-stte dvertisements only in re ech nodes hs detiled re topology; only know direction (shortest pth) to nets in other res. ommunictions between res vi bckbone re border routers: summrize distnces to nets in own re, dvertise to other re order routers. ckbone routers: run OSP routing limited to bckbone. oundry routers: connect to other S s. sci omputer Networks Routing nd Network Lyer Prt II 6 sci omputer Networks Routing nd Network Lyer Prt II 66
Inter-S Routing in the Internet: GP R S (RIP intr-s routing) R GP R R GP S (OSP intr-s routing) igure..-new: GP use for inter-domin routing R S (OSP intr-s routing) Internet inter-s routing: GP GP (order Gtewy Protocol): the de fcto stndrd GP provides ech S mens to:. Obtin subnet rechbility informtion from neighboring Ss.. Propgte the rechbility informtion to ll routers internl to the S.. etermine good routes to subnets bsed on rechbility informtion nd policy. llows subnet to dvertise its existence to rest of the Internet: I m here sci omputer Networks Routing nd Network Lyer Prt II 67 sci omputer Networks Routing nd Network Lyer Prt II 68 GP bsics Pirs of routers (GP peers) exchnge routing info over semipermnent TP conctns: GP sessions Note tht GP sessions do not correspond to physicl links. When S dvertises prefix to S, S is promising it will forwrd ny dtgrms destined to tht prefix towrds the prefix. S cn ggregte prefixes in its dvertisement istributing rechbility info With egp session between nd c, S sends prefix rechbility info to S. c cn then use igp to distribute this new prefix rech info to ll routers in S b cn then re-dvertise the new rech info to S over the b-to- egp session When router lerns bout new prefix, it cretes n entry for the prefix in its forwrding tble. c b S S c b c S b d egp session igp session sci omputer Networks Routing nd Network Lyer Prt II 69 c b S S c b c S b d egp session sci omputer Networks Routing nd Network Lyer Prt II igp session 7 Pth ttributes & GP routes When dvertising prefix, dvert includes GP ttributes. prefix + ttributes = route Two importnt ttributes: S-PTH: contins the Ss through which the dvert for the prefix pssed: S 67 S 7 NT-HOP: Indictes the specific internl-s router to nexthop S. (There my be multiple links from current S to nexthop-s.) When gtewy router receives route dvert, uses import policy to ccept/decline. GP route selection Router my lern bout more thn route to some prefix. Router must select route. limintion rules:. Locl preference vlue ttribute: policy decision. Shortest S-PTH. losest NT-HOP router: hot potto routing. dditionl criteri sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 7
GP messges GP messges exchnged using TP. GP messges: OPN: opens TP connection to peer nd uthentictes sender UPT: dvertises new pth (or withdrws old) KPLIV keeps connection live in bsence of UPTS; lso Ks OPN request NOTIITION: reports errors in previous msg; lso used to close connection W GP routing policy Y legend: igure.-gpnew: simple GP scenrio,, re provider networks,w,y re customer (of provider networks) is dul-homed: ttched to two networks does not wnt to route from vi to.. so will not dvertise to route to provider network customer network: sci omputer Networks Routing nd Network Lyer Prt II 7 sci omputer Networks Routing nd Network Lyer Prt II 7 W GP routing policy () Y legend: provider network customer network: igure.-gpnew: simple GP scenrio dvertises to the pth W dvertises to the pth W Should dvertise to the pth W? No wy! gets no revenue for routing W since neither W nor re s customers wnts to force to route to w vi wnts to route only to/from its customers! sci omputer Networks Routing nd Network Lyer Prt II 7 Why different Intr- nd Inter-S routing? Policy: Inter-S: dmin wnts control over how its trffic routed, who routes through its net. Intr-S: single dmin, so no policy decisions needed Scle: hierrchicl routing sves tble size, reduced updte trffic Performnce: Intr-S: cn focus on performnce Inter-S: policy my dominte over performnce sci omputer Networks Routing nd Network Lyer Prt II 76 Multi-Protocol Lbel Switching (MPLS) initil gol: speed up IP forwrding by using fixed length lbel (insted of IP ddress) to do forwrding borrowing ides from Virtul ircuit (V) pproch but IP dtgrm still keeps IP ddress! PPP or thernet heder MPLS heder lbel IP heder xp S TTL reminder of link-lyer frme MPLS pble Routers.k.. lbel-switched router forwrds pckets to outgoing interfce bsed only on lbel vlue (don t inspect IP ddress) MPLS forwrding tble distinct from IP forwrding tbles signling protocol needed to set up forwrding RSVP-T, LP forwrding possible long pths tht IP lone would not llow (e.g., lest cost pth routing)!! use MPLS for trffic engineering must co-exist with IP-only routers sci omputer Networks Routing nd Network Lyer Prt II 77 sci omputer Networks Routing nd Network Lyer Prt II 78
R6 R MPLS orwrding Tbles in out out lbel lbel dest interfce 8 R R in out out lbel lbel dest interfce 8 6 R in out out lbel lbel dest interfce 6 9 in out R out lbel lbel dest interfce 6 - Why Mobile IP? Need protocol which llows network connectivity cross host movement Protocol to enble mobility must not require mssive chnges to router softwre, etc. Must be comptible with lrge instlled bse of IPv networks/hosts onfine chnges to mobile hosts nd few support hosts which enble mobility sci omputer Networks Routing nd Network Lyer Prt II 79 sci omputer Networks Routing nd Network Lyer Prt II 8 Internet Protocol (IP) Network lyer, "best-effort" pcket delivery Supports UP nd TP (trnsport lyer protocols) IP host ddresses consist of two prts network id + host id y design, IP host ddress is tied to home network ddress Hosts re ssumed to be wired, immobile Intermedite routers look only t network ddress Mobility without chnge in IP ddress results in un-route-ble pckets sci omputer Networks Routing nd Network Lyer Prt II 8 IP Routing reks Under Mobility... 7...*. router router 9...* Why this hierrchicl pproch? nswer: Sclbility! Millions of network ddresses, billions of hosts! sci omputer Networks Routing nd Network Lyer Prt II 8 Mobile IP: sics Proposed by IT (Internet ngineering Tsk orce) Stndrds development body for the Internet Mobile IP llows mobile host to move bout without chnging its permnent IP ddress ch mobile host hs home gent on its home network Mobile host estblishes cre-of ddress when it's wy from home Mobile IP: sics, ont. orrespondent host is host tht wnts to send pckets to the mobile host orrespondent host sends pckets to the mobile host s IP permnent ddress These pckets re routed to the mobile host s s home network Home gent forwrds IP pckets for mobile host to current cre-of ddress Mobile host sends pckets directly to correspondent, using permnent home IP s source IP sci omputer Networks Routing nd Network Lyer Prt II 8 sci omputer Networks Routing nd Network Lyer Prt II 8
Mobile IP: sics, ont. Mobile IP: re-of ddresses correspondent host home gent Whenever mobile host connects to remote network, two choices: cre-of cn be the ddress of foreign gent on the remote network foreign gent delivers pckets forwrded from home gent to mobile bl host cre-of cn be temporry, foreign IP ddress obtined through, e.g., HP home gent tunnels pckets directly to the temporry IP ddress Regrdless, cre-of ddress must be registered with home gent sci omputer Networks Routing nd Network Lyer Prt II 8 sci omputer Networks Routing nd Network Lyer Prt II 86 IP-in-IP Tunneling Pcket to be forwrded is encpsulted in new IP pcket In the new heder: estintion = cre-of-ddress Source = ddress of home gent Protocol number = IP-in-IP IP heder dt IP heder IP heder dt t the Other nd... epending on type of cre-of ddress: oreign gent or Mobile host strips outer IP heder of tunneled pcket, which is then fed to the mobile host side: ny thoughts on dvntges of foreign gent vs. co-locted (foreign IP) ddress? sci omputer Networks Routing nd Network Lyer Prt II 87 sci omputer Networks Routing nd Network Lyer Prt II 88 Routing Inefficiency correspondent host Mobile host nd correspondent host might even be on the sme network!! home gent Route Optimiztions Possible Solution: Home gent sends current cre-of ddress to correspondent host orrespondent host cches cre-of ddress uture pckets tunneled directly to cre-of ddress ut! n instnce of the cche consistency problem rises... ched cre-of ddress becomes stle when the mobile host moves Potentil security issues with providing cre-of ddress to correspondent sci omputer Networks Routing nd Network Lyer Prt II 89 sci omputer Networks Routing nd Network Lyer Prt II 9
Possible Route Optimiztion Network Lyer Prt II Summry Network Lyer Routing sic Issues istributed Routing lgorithms: LS vs. V Link Stte (LS): How does it work? istnce Vector (V): How does it work? Issues? Mobile IP: how does it work? Issues? MPLS Routing in the Internet Intr-S vs. Inter-S routing Intr-S: RIP nd OSP Inter-S: GP nd Policy Routing Things we didn t cover: VPN, IP Multicst, IPv6 (but plese red by yourself!) sci omputer Networks Routing nd Network Lyer Prt II 9 sci omputer Networks Routing nd Network Lyer Prt II 9 6