COMP 631: COMPUTER NETWORKS Inter-domin Routing Jsleen Kur Fll 2014 1 Internet-sle Routing: Approhes DV nd link-stte protools do not sle to glol Internet How to mke routing slle? Exploit the notion of utonomous systems to divide routing into two prts Intr-domin routing: Routing within n utonomous system eg: RIP (distne-vetor type), OSPF (link-stte type) Inter-domin routing: Routing etween utonomous systems Hierrhilly ggregte routing informtion Route propgtion ( know smrter router poliy): Hosts know lol (defult) router Lol routers know site routers Site routers know ore (kone) routers Core routers know everything 2 1
Internet AS-level Arhiteture: Properties Lrge orportion Consumer ISP Peering point Consumer ISP Bkone servie provider Peering point Lrge orportion Consumer ISP Smll orportion Tiered Internet servie providing Multi-homed stu networks Peering reltions Points of presene (POPs) 3 Internet-sle Routing: Chllenges Mtter of sle! Bkone routers must provide mth for ny vlid IP ddress Even with CIDR, still need to mintin O(100,000) prefixes Autonomous nture of domins: Eh domin runs own interior routing protool nd linkost ssignment sheme Impossile to lulte meningful pth osts for pths tht ross multiple domins Therefore, inter-domin routing dvertises only rehility informtion Find ny pth tht is loop-free (optimlity not onsidertion) 4 2
Internet-sle Routing: Chllenges Issue of trust: Provider A my e unwilling to elieve route dvertisements from provider B Misonfigured routers, insuffiient pity to rry trffi, mliious intent Need to support flexile routing poliies: Prevention of trnsit trffi Multi-homed orportions my not wish to rry trffi etween the two providers Provider A my wnt to implement speil poliies: Use provider B only to reh these ddresses Use the pth tht rosses the fewest ASes Use AS x in preferene to AS y Erly-exit poliy! 5 Border Gtewy Protool (BGP) Arhiteturl Components eh AS hs: At lest one BGP speker (spokesperson for entire AS) Estlish BGP sessions to spekers in other ASes Exhnge rehility informtion mong ASes One or more Border Gtewys (through whih pkets enter/leve the AS) Routers hrged with tsk of forwrding pkets etween ASes C. C d A A. A. B. B Border Gtewys 6 3
BGP: Bsi Ide BGP is Pth-vetor protool: Advertises omplete pth for rehing given destintion AS 2 dvertises: networks 128.96, 192.4.153, 192.4.32, 192.4.3 n e rehed diretly from AS 2 Bkone AS dvertises: 128.96, 192.4.153, 192.4.32, 192.4.3 n e rehed long pth: (AS1, AS2) 192.12.169, 192.4.54, 192.4.23 n e rehed long pth: (AS1, AS3) Customer P (AS 4) 128.96 192.4.153 Bkone Provider (AS 1) Regionl Provider A (AS 2) Regionl Provider A (AS 3) Customer Q (AS 5) Customer R (AS 6) Customer S (AS 7) 192.4.32 192.4.3 192.12.169 192.4.54 192.4.23 7 BGP Advertisements: Implementing Poliies Complete AS pth helps implement loop-free routing If AS finds itself in n dvertisement, ignores it An AS will dvertise only those routes tht it onsiders good enough for itself And these re the routes tht it will tully use for forwrding dt BGP spekers need not dvertise routes, even if they know of one Helps implement non-trnsit poliy for multi-homed stu networks If X does not wnt to route trffi to Z, then X will not dvertise ny routes to Z Helps implement ost-relted or usiness-relted poliies Don t dvertise routes vi ompetitor s network (even if ompetitor hs dvertised routes to you) Don t dvertise routes through peers tht hrge you for ytes routed through them 8 4
Putting It Together: Intr-AS & Inter-AS Routing Host h1 C. C d A A. Inter-AS routing etween A nd B A. Intr-AS routing within AS A B. B Intr-AS routing within AS B Host h2 Stu networks send to only order router (if single- homed) Provider AS: Border router injets informzon into the intr- domin rouzng protool I hve link to ustomer- prefix Y of ost X All internl routers send pkets for this desznzon to this order router Bkone AS: Use Interior- BGP (IBGP) to distriute info lerned y BGP spekers to ll routers Enles eh router to lern est order router to use for given prefix 9 Why Different Intr- nd Inter-AS Routing? Poliy: Inter-AS: dministrtion wnts ontrol over how its trffi routed nd who routes through its network Intr-AS: single dministrtion, so no poliy deisions needed Sle: Hierrhil routing sves tle size, redued updte trffi Performne: Intr-AS: n fous on performne Inter-AS: poliy my dominte over performne 10 5
BGP Performne: Pth Reovery 2-yer study of routing updtes y the Routeviews projet Oservtions: Dely in Internet inter-domin pth filovers verges 3 minutes Some lst 15 minutes Cuse: Mostly unforeseen intertion of protool timers with speifi vendor implementtion deisions User-Impt: Filovers ffet end-to-end performne signifintly Mesured pket losses grow y 30 times Lteny grows y 4 times 11 BGP Performne: Misonfigurtions Oservtions mde in 2001 study: Eh dy, 200-1200 prefixes (1% glol BGP tle) suffer misonfigurtions 2% of the time, inreses routing updte lod y t lest 10% One oservtion douled lod ross ll vntge points 3-4 new prefixes seen everydy result from misonfigurtions Cuses: Involuntry slips y network opertors Router initiliztion ugs Poor understnding of onfigurtion semntis y opertors User-impt: onnetivity is roust Only 4% of d nnounements disrupt onnetivity 12 6
BGP Performne: Pth Infltions 2002 study oserved firly inflted pths Cuses: Mny pths tht use erly-exit re inflted (longer RTTs) Topology-insensitive lod lning n use signifint pth infltion Peering points etween ISPs my not e on the shortest pth for two end-hosts Non-erly exit poliies To void ongested peering point Not ll ISPs re diretly onneted to eh other 13 7