Internet Routing. Reminder: Routing. CPSC Network Programming

Transcription

1 PS Network Progrmming Internet Routing Mihele Weigle eprtment of omputer Siene lemson University mweigle@s.lemson.eu pril, 00 Reminer: Routing

2 Internet Routing Hierrhil routing! The theory of routing: reltively simple lgorithms with mngele shortomings! ritil ssumptions: " ll routers re ientil " The network is flt! The relity: Routing is ominte y issues of sle " The Internet hs 00 million hosts!! n t store ll host estintions in routing tles!! Routing tle exhnge woul swmp links! " We must route to networks, not hosts! Routing lso ominte y issues of ministrtive utonomy " The Internet is network of networks eh network owner my wnt to ontrol routing in its own network Hierrhil Routing Gtewy routers! ggregte routers into regions, utonomous systems (S)! ll routers insie sme S run sme routing protool mong themselves " Intr-S routing protool "Routers in ifferent S n run ifferent intr-s routing protool Gtewy routers! Speil routers in S! Run intr-s routing protool with ll other routers insie S! Responsile for routing to estintions outsie S " lso run inter-s routing protool with gtewy routers in jent S

3 Hierrhil Routing Intr-S & Inter-S Routing....! Gtewys: "Perform inter-s routing mong themselves "Perform intr-s routing with other routers in their S Inter-S n intr-s routing in gtewy. Intr-S Routing lgorithm Routing Tle Inter-S Routing lgorithm network lyer link lyer physil lyer to/from. L PHY L PHY to/from. L PHY to/from. Hierrhil Routing Intr-S & Inter-S Routing Host h... Intr-S routing within S Inter-S routing etween n. Host h Intr-S routing within S! We ll exmine speifi inter-s n intr- S Internet routing protools shortly

4 Routing on the Internet The Internet S hierrhy Inter-S orer (exterior gtewy) routers.... Intr-S (interior gtewy) routers The Internet S Hierrhy Intr-S routing....! lso known s Interior Gtewy Protools (IGPs)! Most ommon IGPs: "RIP: Routing Informtion Protool "OSPF: Open Shortest Pth First "IGRP: Interior Gtewy Routing Protool (iso proprietry)

5 RIP (istne-vetor Flshk)! Eh noe hs its own tle " Row for eh possile estintion " olumn for eh iretly-tthe jent noe (neighor)! Eh tle entry gives ost to reh estintion vi tht jent noe " istne = ost estintion E () ost to estintion vi X (Y,Z) = istne from X to Y vi Z s first hop = (X,Z) + min w { Z (Y,w)} w = {neighors of Z} RIP (istne-vetor Flshk) 7 E 8! The istne tle gives the routing tle " Just tke the minimum ost per estintion estintion istne Tle E () Routing Tle E () estintion,,, 4, jent Noe to Use, ost

6 Intr-S routing RIP! istne vetor-like lgorithm " ommonly use in the erly Internet! istne metri: Numer of hops " Mximum vlue = hops (! = 6)! Routing tles (inluing osts) re exhnge with jent noes every 30 seons vi Response Messge (lso lle route vertisement ) " Reeiver etermines if jent noe hs foun new minimum ost to estintion! Eh vertisement onsists of the minimum ost route for up to estintion networks Intr-S routing IGRP! ISO proprietry; suessor of RIP (mi 80s)! istne Vetor-like similr to RIP "Severl ost metris: ely, nwith, reliility, lo, et. "Uses TP to exhnge routing uptes

7 OSPF (Link-Stte Flshk)! Uses ijkstr s shortest pth grph lgorithm! omplete network topology n link osts known t ll noes " omplishe vi link stte flooing " ll noes lern the sme topology n ost t! Eh noe omputes lest ost pths from itself to ll other noes " Proues routing tle for tht noe 3 " ll noes ompute onsistent routing tles 3 E F Intr-S routing OSPF! Open : pulily ville!uses the Link Stte minimum ost pth omputtion lgorithm "LS upte flooing "Topology mp t eh noe "Route omputtion using ijkstr s lgorithm! OSPF vertisement rries one entry per jent noe! vertisements isseminte to n entire S (vi flooing)

8 OSPF Hierrhil OSPF To other S OSPF Hierrhil OSPF! Two-level hierrhy: lol re, kone "Link-stte vertisements only in re "Eh re noe hs etile re topology; only knows shortest pth to networks in other res! re orer Routers: summrize istnes to nets in own re n vertise to other re orer routers! kone Routers: run OSPF routing limite to kone! ounry Routers: onnet to other S

9 The Internet S Hierrhy Inter-S Routing...! orer Gtewy Protool (GP) is the e fto stnr! Pth Vetor protool: " Similr to istne Vetor protool " Eh orer Gtewy vertises to jent noes (peers) the entire pth (i.e., sequene of S numers) to estintion " e.g., Gtewy X my sen its pth to estintion Z: pth (X,Z) = X, Y, Y, Y3,, Z. The Internet S Hierrhy Why ifferent intr- n inter-s routing?! Poliy: "Inter-S: ministrtion wnts ontrol over how its trffi route n who routes through its network "Intr-S: single ministrtion, so no poliy eisions neee! Sle: "Hierrhil routing sves tle size, reue upte trffi! Performne: "Intr-S: n fous on performne "Inter-S: poliy my ominte over performne