Gols of Routing Protocols 10: Inter nd intr AS, RIP, OSPF, GP, Router Architecture Lst Modified: 3/24/2003 2:39:16 PM Find the optiml route Rpid Convergence Robustness Configurble to respond to chnges in mny vribles (chnges in bndwidth, dely, queue size, policy, etc.) Ese of configurtion 4: Network Lyer 4-1 4: Network Lyer 4-2 Rel Internet Routing? CIDR? Dynmic routing protocols running between every router? Recll CIDR We lredy tlked bout how routing bsed on hierrchicl lloction of IP ddress spce cn llows efficient dvertisement of routing informtion: Orgniztion 0 200.23.16.0/23 Orgniztion 1 200.23.18.0/23 Orgniztion 2 200.23.20.0/23 Orgniztion 7. 200.23.30.0/23.. Fly-y-Night-ISP ISPs-R-Us Send me nything with ddresses beginning 200.23.16.0/20 Send me nything with ddresses beginning 199.31.0.0/16 Internet 4: Network Lyer 4-3 4: Network Lyer 4-4 CIDR? Dynmic Routing? CIDR by itself is nice ide but.. Hrd to mintin Work round existing IP ddress spce lloctions Wht bout redundnt pths? Dynmic routing protocols? They mintin/updte themselves Allow for redundnt pths ut could every router in the Internet be node in the grph? Dynmic Routing Protocols? Our study of dynmic routing protocols thus fr = idelized grph problem ll routers identicl network flt not true in prctice scle: with 50 million destintions: cn t store ll destintions in routing tbles! routing tble exchnge would swmp links! Neither link stte nor distnce vector could hndle the whole Internet! 4: Network Lyer 4-5 4: Network Lyer 4-6
Routing in the Internet Administrtive Autonomy Internet = network of networks Ech network controls routing in its own network Globl routing system to route between Autonomous Systems (AS) Two-level routing: Intr-AS: dministrtor is responsible for choice Inter-AS: unique stndrd Hierrchicl Routing Routers in sme AS run routing protocol chosen by dministrtors of tht domin intr-as routing protocol routers in different AS cn run different intr- AS routing protocol gtewy routers specil routers in AS run intr-as routing protocol with ll other routers in AS lso responsible for routing to destintions outside AS run inter-as routing protocol with other gtewy routers 4: Network Lyer 4-7 4: Network Lyer 4-8 Internet AS Hierrchy Intr-AS nd Inter-AS routing Intr-AS border (exterior gtewy) routers C.b b C d A A. b A.c c. c Gtewys: perform inter-as routing mongst themselves b perform intr-as routers with other routers in their AS Inter-AS interior (gtewy) routers inter-as, intr-as routing in gtewy A.c network lyer link lyer physicl lyer 4: Network Lyer 4-9 4: Network Lyer 4-10 Intr-AS nd Inter-AS routing Inter-AS C.b routing between A. A nd b A.c C Host d h1 c A b Intr-AS routing within AS A. Host c h2 b Intr-AS routing within AS Single dtgrm is often routed over mny hops vi routes estblished by severl intr-as routing protocols nd n inter-as routing protocol 4: Network Lyer 4-11 Intr vs Inter AS Routing protcols For Intr AS routing protocols: mny choices; For Inter AS routing protocols: stndrd Why does this mke sense? Intr AS routing protocols focus on performnce optimiztion; Inter AS routing protocols focus on dministrtive issues Why does this mke sense? Choice in Intr-AS Intr-AS often sttic routing bsed on CIDR, cn lso be dynmic (usully RIP or OSPF) Stndrd Inter-AS GP is dynmic 4: Network Lyer 4-12
Intr-AS Routing RIP ( Routing Informtion Protocol) Also known s Interior Gtewy Protocols (IGP) Most common IGPs: RIP: Routing Informtion Protocol OSPF: Open Shortest Pth First IGRP: Interior Gtewy Routing Protocol (Cisco proprietry) Cn lso be sttic (vi CIDR) but tht is not clled n IGP Distnce vector lgorithm Included in SD-UNIX Distribution in 1982 Single Distnce metric: # of hops (mx = 15 hops) Cn you guess why? Count to infinity less pinful if infinity = 16 ut limits RIP to networks with dimeter of 15 hops Distnce vectors: exchnged every 30 sec vi Response Messge (lso clled dvertisement) Ech dvertisement: route to up to 25 destintion nets 4: Network Lyer 4-13 4: Network Lyer 4-14 RIP: Link Filure nd Recovery If no dvertisement herd fter 180 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 smll loops infinite distnce = 16 hops to mke mke problem with lrger loops less pinful RIP Tble processing RIP routing tbles mnged by ppliction-level process clled route-d (demon) dvertisements sent in UDP pckets, periodiclly repeted Periodiclly inform kernel of routing tble to use 4: Network Lyer 4-15 4: Network Lyer 4-16 RIP Tble exmple: netstt -rn OSPF (Open Shortest Pth First) Destintion Gtewy Flgs Ref Use Interfce -------------------- -------------------- ----- ----- ------ --------- 127.0.0.1 127.0.0.1 UH 0 26492 lo0 192.168.2. 192.168.2.5 U 2 13 f0 193.55.114. 193.55.114.6 U 3 58503 le0 192.168.3. 192.168.3.5 U 2 25 q0 224.0.0.0 193.55.114.6 U 3 0 le0 defult 193.55.114.129 UG 0 143454 Three ttched clss C networks (LANs) Router only knows routes to ttched LANs Defult router used to go up Route multicst ddress: 224.0.0.0 Loopbck interfce (for debugging) 4: Network Lyer 4-17 open : publicly vilble Uses Link Stte lgorithm LS pcket dissemintion Topology mp t ech node Route computtion using Dijkstr s lgorithm OSPF dvertisement crries one entry per neighbor router (i.e. cost to ech neighbor) Advertisements disseminted to entire AS (vi flooding) 4: Network Lyer 4-18
OSPF dvnced fetures (not in RIP) Hierrchicl OSPF: Mini Internet Mny hve nothing to do with link-stte vs distnce vector!! Security: ll OSPF messges uthenticted (to prevent mlicious intrusion); TCP connections used Multiple sme-cost pths cn be used t once (single pth need not be chosen s in RIP) For ech link, multiple cost metrics for different TOS (eg, high W, high dely stellite link cost my set low for best effort; high for rel time) Integrted uni- nd multicst support: Multicst OSPF (MOSPF) uses sme topology dt bse s OSPF Hierrchicl OSPF in lrge domins Within ech re, border router responsible for routing outside the re Exctly one re is bckbone re ckbone re contins ll re border routers nd possibly others Full brodcst in ech sub domin only 4: Network Lyer 4-19 4: Network Lyer 4-20 Hierrchicl OSPF 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. Are border routers: summrize distnces to nets in own re, dvertise to other Are order routers. ckbone routers: run OSPF routing limited to bckbone. oundry routers: connect to other ASs. IGRP (Interior Gtewy Routing Protocol) CISCO proprietry; successor of RIP (mid 80s) Distnce Vector, like RIP but with dvnced fetures like OSPF severl cost metrics (dely, bndwidth, relibility, lod etc); dminister decides which cost metrics to use uses TCP to exchnge routing updtes Loop-free routing vi Distributed Updting Alg. (DUAL) bsed on diffused computtion 4: Network Lyer 4-21 4: Network Lyer 4-22 Now on to Inter-AS routing Autonomous systems The Globl Internet consists of Autonomous Systems (AS) interconnected with ech other: Stub AS: smll corportion Multihomed AS: lrge corportion (no trnsit trffic) Trnsit AS: provider (crries trnsit trffic) Mjor gol of Inter-AS routing protocol is to reduce trnsit trffic 4: Network Lyer 4-23 4: Network Lyer 4-24
Internet inter-as routing: GP Internet inter-as routing: GP GP (order Gtewy Protocol): the de fcto stndrd Pth Vector protocol: similr to Distnce Vector protocol Avoids count-to-infinity problem by identifying yourself in pth dvertised to you ech order Gtewy brodcst to neighbors (peers) entire pth (I.e, sequence of ASs) to destintion E.g., Gtewy X my send its pth to dest. Z: Suppose: gtewy X send its pth to peer gtewy W W my or my not select pth offered by X cost, policy (don t route vi competitors AS!), loop prevention resons. If W selects pth dvertised by X, then: Pth (W,Z) = w, Pth (X,Z) Note: X cn control incoming trffic by controlling its route dvertisements to peers: e.g., don t wnt to route trffic to Z -> don t dvertise ny routes to Z Pth (X,Z) = X,Y1,Y2,Y3,,Z 4: Network Lyer 4-25 4: Network Lyer 4-26 Internet inter-as routing: GP Internet Mp GP messges exchnged using TCP. GP messges: OPEN: opens TCP connection to peer nd uthentictes sender UPDATE: dvertises new pth (or withdrws old) KEEPALIVE keeps connection live in bsence of UPDATES; lso ACKs OPEN request NOTIFICATION: reports errors in previous msg; lso used to close connec tion Now tht we know bout utonomous systems nd intr nd inter AS routing protocols Wht does the Internet relly look like? Tht is ctully hrd question to nswer Internet Atls Project http://www.cid.org/projects/internettls/ Techniques, softwre, nd protocols for mpping the Internet, focusing on Internet topology, performnce, worklod, nd routing dt 4: Network Lyer 4-27 4: Network Lyer 4-28 The Internet round 1990 CAIDA: NSFNET growth until 1995 ckbone nodes elevted 4: Network Lyer 4-29 Low Trffic Volume High 4: Network Lyer 4-30
NSF Networking Architecture of Lte 1990s NSFNET ckbone Project successfully trnsitioned to new networking rchitecture in 1995. vns ( very high speed ckbone Network Services) - NSF funded, provided by MCI 4 originl Network Access Points (NSF wrded) NSF funded Routing Arbiter project Network Service Providers (not NSF funded) Network Access Point Allows Internet Service Providers (ISPs), government, reserch, nd eductionl orgniztions to interconnect nd exchnge informtion ISPs connect their networks to the NAP for the purpose of exchnging trffic with other ISPs Such exchnge of Internet trffic is often referred to s "peering" 4: Network Lyer 4-31 4: Network Lyer 4-32 The Internet in 1997 CAIDA s skitter plot Loction (longitude) Top 15 ASes re in North Americ (14 in US, 1 in Cnd) Highly connected Mny links US to Asi nd Europe; few direct Asi/Europe Links Asi Few connections Europe Skitter dt 16 monitors probing pproximtely 400,000 destintions 626,773 IP ddresses 1,007.723 IP links 48,302 (52%) of globlly routble network prefixes 4: Network Lyer 4-33 North Americ 4: Network Lyer 4-34 Economics of Internet Connectivity Upstrem ISPs chrge downstrem ISPs for connectivity (trnsit trffic) Downstrem ISPs chnge customers Upper level ISPs exchnge trffic t NAPs for mutul convenience Rodmp Mechnics of Routing Sending dtgrm to destintion on sme network Sending dtgrm to destintion on different network Router Architecture Router Configurtion Demo 4: Network Lyer 4-35 4: Network Lyer 4-36
Getting dtgrm from source to dest. IP dtgrm: misc fields source IP ddr dest IP ddr dt dtgrm remins unchnged, s it trvels source to destintion ddr fields of interest here A routing tble in A Dest. Net. next router Nhops 223.1.1 1 223.1.2 223.1.1.4 2 223.1.3 223.1.1.4 2 223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.2.9 223.1.1.3 223.1.3.1 223.1.2.2 223.1.3.27 E 223.1.3.2 Destintion on sme network s source misc fields 223.1.1.1 223.1.1.3 dt Strting t A, given IP dtgrm ddressed to : look up net. ddress of find is on sme net. s A link lyer will send dtgrm directly to inside link-lyer frme nd A re directly connected A Dest. Net. next router Nhops 223.1.1 1 223.1.2 223.1.1.4 2 223.1.3 223.1.1.4 2 223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.2.9 223.1.1.3 223.1.3.1 223.1.2.2 223.1.3.27 E 223.1.3.2 4: Network Lyer 4-37 4: Network Lyer 4-38 Destintion on different network thn source, Step 1 misc fields 223.1.1.1 223.1.2.3 dt Strting t A, dest. E: look up network ddress of E E on different network A, E not directly ttched routing tble: next hop router to E is 223.1.1.4 link lyer sends dtgrm to router 223.1.1.4 inside linklyer frme dtgrm rrives t 223.1.1.4 continued.. A Dest. Net. next router Nhops 223.1.1 1 223.1.2 223.1.1.4 2 223.1.3 223.1.1.4 2 223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.2.9 223.1.1.3 223.1.3.1 223.1.2.2 223.1.3.27 E 223.1.3.2 4: Network Lyer 4-39 Destintion on different network thn source, Step 2 Dest. next misc fields 223.1.1.1 223.1.2.3 dt network router Nhops interfce 223.1.1-1 223.1.1.4 Arriving t 223.1.4, 223.1.2-1 223.1.2.9 destined for 223.1.2.2 223.1.3-1 223.1.3.27 look up network ddress of E A 223.1.1.1 E on sme network s router s interfce 223.1.2.9 router, E directly ttched 223.1.1.2 223.1.1.4 223.1.2.1 223.1.2.9 link lyer sends dtgrm to 223.1.2.2 inside link-lyer 223.1.1.3 223.1.3.27 223.1.2.2 E frme vi interfce 223.1.2.9 223.1.3.1 223.1.3.2 dtgrm rrives t 223.1.2.2!!! (hoory!) 4: Network Lyer 4-40 Router Architecture Overview Two key router functions: run routing lgorithms/protocol (RIP, OSPF, GP) switching dtgrms from incoming to outgoing link Input Port Functions Physicl lyer: bit-level reception Dt link lyer: e.g., Ethernet Decentrlized switching: given dtgrm dest., lookup output port using routing tble in input port memory gol: complete input port processing t line speed queuing: if dtgrms rrive fster thn forwrding rte into switch fbric 4: Network Lyer 4-41 4: Network Lyer 4-42
Input Port Queuing Three types of switching fbrics Fbric slower tht input ports combined -> queueing my occur t input queues Hed-of-the-Line (HOL) blocking: queued dtgrm t front of queue prevents others in queue from moving forwrd queueing dely nd loss due to input buffer overflow! 4: Network Lyer 4-43 4: Network Lyer 4-44 Switching Vi Memory First genertion routers: pcket copied by system s (single) CPU speed limited by memory bndwidth (2 bus crossings per dtgrm) Input Port Modern routers: Memory Output Port System us input port processor performs lookup, copy into memory Exmple: Cisco Ctlyst 8500 4: Network Lyer 4-45 Switching Vi us dtgrm from input port memory to output port memory vi shred bus bus contention: switching speed limited by bus bndwidth 1 Gbps bus (Exmple: Cisco 1900): sufficient speed for ccess nd enterprise routers (not regionl or bckbone) 4: Network Lyer 4-46 Switching Vi An Interconnection Network Output Ports overcome bus bndwidth limittions nyn networks, other interconnection nets initilly developed to connect processors in multiprocessor Consider things like cross sectionl W Used s interconnection network in the router insted of simple crossbr Advnced design: frgmenting dtgrm into fixed length cells, switch cells through the fbric. Exmple: Cisco 12000 switches Gbps through the interconnection network uffering required when dtgrms rrive from fbric fster thn the trnsmission rte Scheduling discipline chooses mong queued dtgrms for trnsmission 4: Network Lyer 4-47 4: Network Lyer 4-48
Output port queueing Router Hrdwre buffering when rrivl rte vi switch exceeds ouput line speed queueing (dely) nd loss due to output port buffer overflow! 4: Network Lyer 4-49 4: Network Lyer 4-50 Router Configurtion Outtkes Router Softwre: operting system with built in pplictions (commnd line interpreters, web servers) Configure Ech Interfce Configure Routing Protocol 4: Network Lyer 4-51 4: Network Lyer 4-52 A typicl Network Access Point (NAP) A smll Internet router MCI Pc.ell link ol.com Division A FDDI ADSU = ATM Dt Service Unit IDSU = Intelligent Dt Service Unit 4: Network Lyer 4-53 ethernet host Division 4: Network Lyer 4-54
Why different Intr- nd Inter-AS routing? Policy: Inter-AS: dmin wnts control over how its trffic routed, who routes through its net. Intr-AS: single dmin, so no policy decisions needed Scle: hierrchicl routing sves tble size, reduced updte trffic Performnce: Intr-AS: cn focus on performnce Inter-AS: policy my dominte over performnce CAIDA: Lyout showing Mjor ISPs 4: Network Lyer 4-55 4: Network Lyer 4-56