SCALABLESCALABLE Ankit Singla, P. Brighten Godfrey Kevin Fall, Sylvia Ratnasamy, Gianluca Iannaccone ON

Scalable Routing N UMBER OF N ODES = n N OT V ERY S CALABLE ! S HORTEST -P ATH R OUTING ? R OUTING S TATE /N ODE

Scalable Routing S TRUCTURED T OPOLOGIES 3 4, 11 6, 20 But, what about general topologies?

Scalable Routing H IERARCHY Inefficient Location-dependent addressing s t 4

Why Not DNS/DHTs? Arbitrarily long paths! 5 W HERE IS A? A R IGHT N EXT TO Y OU, S ILLY !

Local Name Resolution Why local name-resolution matters – Google: 400ms delay = 0.59% searches/user – Time for name-resolution is a significant fraction of latency for short flows (which are the majority) – Fate sharing property 6

Arbitrary names – independent of location Useful primitive – Mobility – Security – Simplified management 7 Flat Names

Another Way to Scale Compact Routing – [Thorup & Zwick ’01, Abraham et al. ’04] – Idea: accept (slightly) longer paths, get lower state – State => Stretch 8

... Compact Routing N UMBER OF N ODES = n R OUTING S TATE /N ODE 9

Algorithm != Protocol N OT DISTRIBUTED N OT DYNAMIC 10

Disco 11 * Assumption: partial source routes are of size O(polylog(n))..

Disco Local Name Resolution Name Resolution NDDisco: Name-Dependent Distributed Compact Routing 12

NDDisco 13 s Addr (t) = (L(t), b, t) t L(t) b

NDDisco 14 s t' L(t') For nearby nodes, the approximation can be poor!

NDDisco 15 s t' L(t) t

NDDisco 16 s L(t) Destination can help! t

Disco Local Name Resolution Name Resolution NDDisco: Name-Dependent Distributed Compact Routing Name Resolution 17

Name Resolution Name -> Address mappings stored in DHT over landmarks Similar to prior work [BVR, S4] Arbitrarily high stretch for address lookup! 18 s t

Disco Local Name Resolution Name Resolution NDDisco: Name-Dependent Distributed Compact Routing Local Name Resolution 19

Local Name Resolution t s 20 ? L(t) Smells like hash functions!

Sloppy Groups Increasing h() E VERYONE A GREES ON T HIS P ART t G(t) 21

Address Dissemination Requirements: – Low diameter for quick dissemination of addresses – Low messaging overhead – Fault tolerance Increasing h() 22

Address Dissemination Predecessor, successor and small O(1) number of fingers Distance-vector style dissemination of addresses 23 Increasing h()

1: Overlay Topology Predecessor, successor and small O(1) number of fingers – Fault tolerance: Use landmarks to fix overlay when broken – Miserly messaging: each node hears each address O(1) times – We don’t care about routing, only diameter, which is small! Increasing h() 24

2: Dissemination Protocol Disseminate new addresses learnt to overlay neighbors Record where each address was learnt from (distance vector-like) Always forward away from the direction received from – Avoids count-to-infinity problem because of ordered space Increasing h() 25

Handling Failures: Example No soft-state required! Update only on changes Increasing h() G ET N EW N EIGHBOR F ROM L ANDMARK W ITHDRAW A DDRESSES L EARNT FROM X 26 X

Routing in Disco 27 w(t) s computes h(t) w(t) = Longest-prefix match for h(t) in Vicinity(s) First : s w(t) L(t) t Later: s L(t) t s t L(t)

Protocol Messages Estimating ‘n’: synopses exchanged with neighbors Landmark and Vicinity updates: path vector style Sloppy-group bootstrap through landmarks Address-dissemination: distance-vector style 28 s

Summary 29

Evaluation Protocols – Disco – NDDisco – S4 [Mao et al ‘07] – VRR [Caesar et al ‘06] refer to paper Topologies – Router-level Internet topology (n = 192,244) – AS-level Internet topology (n = 30,610) – Geometric random graphs, mean degree 8 – G(n, m), mean degree 8 30

State S HORTEST P ATH P ROTOCOL 31 NDD ISCO S4 G EOMETRIC R ANDOM G RAPHS OF I NCREASING S IZE

State 32 L ONG T AIL S4 D ISCO NDD ISCO R OUTER -L EVEL I NTERNET T OPOLOGY

First-Packet Stretch G EOMETRIC RANDOM GRAPH NODES R OUTER -L EVEL I NTERNET T OPOLOGY L ARGE F IRST -P ACKET S TRETCH D ISCO S4 D ISCO L IMITED BY S MALL P ATH - LENGTHS IN T OPOLOGY

Later-Packets Stretch G EOMETRIC RANDOM GRAPH NODES R OUTER -L EVEL I NTERNET T OPOLOGY 34 D ISCO < 1.2 N EAR -I DENTICAL S4 D ISCO

Are the Landmarks Clobbered? AS-L EVEL I NTERNET T OPOLOGY 35 ~4 IN EVERY 10,000 EDGES SEE MORE CONGESTION D ISCO

Conclusion 36

Thank You Questions?