Internet Routing. IP Packet Format. IP Fragmentation & Reassembly. Principles of Internet Routing. Computer Networks 9/29/2014.

Transcription

1 omputer Networks 9/29/2014 IP Pket Formt Internet Routing Ki Shen IP protool version numer heder length (words) for qulity of servie mx numer remining hops (deremented t eh router) upper lyer protool to deliver pylod to IP heder size? 32 its ver hed. type of len servie length 16-it identifier flgs frgment offset time to upper heder live lyer heksum 32-it soure IP ddress 32-it destintion IP ddress Options (if ny) dt (vrile length, typilly TP or UDP segment) totl dtgrm length (ytes) for frgmenttion/ ressemly e.g. timestmp, reord route tken. 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll IP Frgmenttion & Ressemly Priniples of Internet Routing Network links hve MTU lrgest possile frme. different link types, different MTUs Lrge IP pket divided ( frgmented ) in one pket eomes severl pkets ressemled only t finl destintion IP heder its used to identify, order relted frgments ressemly frgmenttion: in: one lrge pket out: 3 smller pkets Our routing study thus fr ideliztion uniform routing sheme ross whole uniform optimiztion gol does not work well in prtie sle: with hundreds of millions of destintions: n t store ll dest s in routing tles! routing tle exhnge would swmp links! dministrtive utonomy internet = of s eh dmin my wnt to ontrol routing in its own 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll

2 omputer Networks 9/29/2014 Hierrhil Routing The Glol Internet onsists of utonomous Systems (S) interonneted with eh other Eh S is usully the of one orgniztion without internl onflit of interests Two level routing: Intr S: dministrtor responsile for hoie of routing lgorithm within, typilly optimized for performne Inter S: unique stndrd to onnet ll Ses, performne my not e the only gol Hierrhil Routing One pth n onsist multiple route domins with different routing protools Host h1 Inter-S. routing etween. nd. d Intr-S routing within S. Host h2 Intr-S routing within S 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll Gtewy Routers utonomous Systems in Prtie. d... Gtewys: perform inter S routing mongst themselves perform intr S routing with other routers in their S Types of utonomous Systems (S): Stu S: smll orportion: one onnetion to other S s Multihomed S: lrge orportion (no trnsit): multiple onnetions to other S s Trnsit S: provider, hooking mny S s together inter-s, intr-s routing in gtewy. lyer link lyer physil lyer See list of Ses 7 9/29/2014 S 257/457 - Fll

3 omputer Networks 9/29/2014 RIP: n Intr S Routing Protool RIP ( Routing Informtion Protool) Distne vetor routing lgorithm For slility, eh entry in routing tle typilly represents Distne metri: # of hops Routing tles exhnged (route dvertisement) mong neighors periodilly (e.g., every 30 ses) why not stop fter onverging? 9/29/2014 S 257/457 - Fll RIP: Exmple w x y D Destintion Network Next Router Num. of hops to dest. w 2 y 2 z 7 x Routing tle in D 9/29/2014 S 257/457 - Fll z RIP: Exmple Routing Tle Exmple Dest Next hops w - - x - - z dvertisement from to D w x y D z hek routing tle t your own worksttion: netstt -rn Destintion Gtewy Interfe / eth / eth eth0 Routing tle in D: Destintion Network Next Router Num. of hops to dest. w 2 y 2 z 7 5 x /29/2014 S 257/457 - Fll Lol IP ontins two segments of IP ddresses Routing tles in routers re more omplex 9/29/2014 S 257/457 - Fll

4 omputer Networks 9/29/2014 OSPF: nother Intr S Routing Protool OSPF (Open Shortest Pth First) Uses Link Stte lgorithm Disseminte link stte informtion to entire S omplete topology mp t eh node Route omputtion using Dijkstr s lgorithm Solve the slility prolem in OSPF Hierrhil OSPF in lrge S Hierrhil OSPF Two level hierrhy: lol re, kone. Link stte rodsts only in re Eh node hs detiled re topology Routers: re order routers: run intr re OSPF routing s well s kone OSPF routing. kone routers: run OSPF routing limited to kone. oundry routers: onnet to other S s. 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll Inter S Routing in the Internet GP Routing Protool R5 S1 (RIP intr-s R1 Inter-S R2 Inter-S R3 S2 (OSPF intr-s R4 S3 (OSPF intr-s There should e just one inter S routing protool GP (order Gtewy Protool) Inter S routing ross multiple dministrtive domins, whih n hve onfliting interests Pth Vetor protool: similr to Distne Vetor protool eh order Gtewy rodst to neighors (peers) entire pth (i.e., sequene of S s) to destintion Flexile routing mngement in GP router selets routes offered y neighors sed on ost poliy (don t route vi ompetitors S) router n ontrol inoming trffi y mnipulting its route dvertisements to neighors: e.g., don t wnt to route trffi from Z > don t dvertise ny routes to Z 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll

5 omputer Networks 9/29/2014 GP Routing Poliy Mngement GP Routing Tle W,, re provider s X,W,Y re ustomers (of provider s), X is dul homed X does not wnt to route trnsit trffi etween nd X dvertises nothing to or wnts to help its ustomer (W) ut not irrelevnt trffi tells W everything it knows tells, out link to W ut not link to, X Y legend: provider ustomer : 9/29/2014 S 257/457 - Fll GP routing tle t n S reords omplete pths to ll other Ses See n exmple Possile to onstrut (lmost) omplete internet topology (S level) with GP routing tles from severl routers 9/29/2014 S 257/457 - Fll Why two level Intr nd Inter S routing? Dislimer Sle: Hierrhil routing sves tle size, redues updte trffi Poliy vs. performne: Inter S: dmin wnts ontrol over how its trffi routed, who routes through its. Performne in glol sense is not mjor onern for individul servie provider. Intr S: single dmin, n fous on performne. Prts of the leture slides ontin originl work of Jmes Kurose, Lrry Peterson, nd Keith Ross. The slides re intended for the sole purpose of instrution of omputer s t the University of Rohester. ll opyrighted mterils elong to their originl owner(s). 9/29/2014 S 257/457 - Fll /29/2014 S 257/457 - Fll