RON Resilient Overlay Networks David Andersen Hari Balakrishnan
RON: Resilient Overlay Networks David Andersen, Hari Balakrishnan, Frans Kaashoek, and Robert Morris MIT Laboratory for Computer Science http: //nms. lcs. mit. edu/ron/
Fault-tolerant networking B A Network C D • Packet switching and route around failures
Internet: network of networks Site 2 Site 3 ISP 1 ISP 2 Site 1 ISP 3 Site 5 • ISPs peer to forward packets • ISP exchange route info using BGP Site 4
The Internet is ill suited to mission-critical applications • Commercial peer architecture – Performance bottlenecks at peering points – Ignores many existing alternate paths – Directly conflicts with robustness • Internet’s global scale: – Prevents sophisticated algorithms – Route selection uses fixed, simple metrics – Routing isn’t sensitive to path quality
How robust is Internet routing? Paxson 95 -97 • 3. 3% of all routes had serious problems Labovitz 97 -00 • 10% of routes available < 95% of the time • 65% of routes available < 99. 9% of the time • 3 -min minimum detection+recovery time; often 15 mins • 40% of outages took 30+ mins to repair Chandra 01 • 5% of faults last more than 2. 75 hours
Our goal To improve communication availability for small groups by at least a factor or 10 • Many applications – Collaboration and conferencing – Virtual Private Networks (VPNs) across public Internet – Overlay Internet Service
Overlay routes around Internet failures Utah Company MIT Cable Modem • Failures: –Outages: Configuration/operational errors, backhoes, etc. –Performance failures: Severe congestion, denial-of-service attacks, etc.
Scalability versus recovery • Internet scalability pays a price: – Slow recovery • RON recovers fast by – Limiting size of overlay – Exploiting redundancy in underlying Internet
Redundant links • Multiple paths between all sites Utah Company Internet 2 MIT Cable Modem
Redundant links • But many of them are hidden Utah Company MIT Cable Modem
Resilient overlay networks • • Measure all links between nodes Compute path properties Determine best route Forward traffic over that path
RON design Nodes in different routing domains (ASes) RON library Conduit Forwarder Prober Router Conduit Performance Database Forwarder Prober Router Application-specific routing tables Policy routing module
Routing and path selection • Path selection at the entry node – Specialized for routing through one intermediate node • Router computes the forwarding tables – Link-state dissemination through RON • Path evaluation and selection – Latency minimizer: EWMA of round-trip samples – Loss-rate minimizer: average of the last k samples – Throughput optimizer: TCP throughput equation • Select when estimated throughput improves by 2 x • 5% hysteresis to avoid flapping
Policy routing • Router computes a forwarding table for each policy • Two ways of describing policies: – Exclusive cliques (e. g. , educational only) – General policies • BPF-like packet matcher, which returns a policy • Links that are denied by a policy • Entry node classifies packet with a policy tag
Responding to failure • Probe interval: 12 seconds • Probe timeout: 3 seconds • Routing update interval: 14 seconds
RON overhead 10 nodes 1. 8 Kbps 20 nodes 5. 9 Kbps 30 nodes 12 Kbps 40 nodes 21 Kbps 50 nodes 32 Kbps • Probe overhead: 69 bytes • RON routing overhead: 60 + 20 (N-1) • 50: allows recovery times between 12 and 25 s
Many research questions • Does the RON approach work at all? • Each RON is small in size, no more than 50 or 100 nodes – How fast can failure detection & recovery happen? • Policy routing – Doesn’t RON violate AUPs and other policies? • Routing behavior – Can stable routing be achieved? – Implementing efficient multi-criteria routing • Is it safe to deploy a large number of (small) interacting RONs on the Internet?
IP forwarder • A RON application • Transparently forwards IP traffic over RON • Allows comparisons of IP traffic over RON versus over direct Internet
RON deployment (19 sites) To vu. nl lulea. se ucl. uk To kaist. kr, . ve . com (ca), dsl (or), cci (ut), aros (ut), utah. edu, . com (tx) cmu (pa), dsl (nc), nyu , cornell, cable (ma), cisco (ma), mit, vu. nl, lulea. se, ucl. uk, kaist. kr, univ-in-venezuela
AS view
Experiments • Measure loss, latency, and throughput with and without RON • RON 1: 12 hosts in the US and Europe – 64 hours of measurements in March 2001 • RON 2: 16 hosts – 85 hours of measurements in May 2001 • 30 -minute average loss rates – A 30 minute outage is very serious! • Note: Experiments done with “No-Internet 2 -forcommercial-use” policy
Take home messages 1. RON reduced outages by a factor 5 to 10, and routed around all major outages 2. RON takes 18 s (average) to route around a failure, and can do so in the face of flooding attacks 3. Single route indirection delivers the majority RON benefits
30 -min average loss rate on Internet RON improves loss-rate RON loss rate never more than 30% 13, 000 samples 30 -min average loss rate with RON
An order-of-magnitude fewer failures 30 -minute average loss rates Loss Rate 10% 20% 30% 50% 80% 100% RON Better 526 [517] 142 [140] 32 [32] 20 [20] 14 [14] 10 No Change 58 [51] 4 [3] 0 0 RON Worse 47 [45] 15 [15] 0 0 6, 825 “path hours” represented here 12 “path hours” of essentially complete outage 72 “path hours” of TCP outage RON routed around all of these! One indirection hop provides almost all the benefit!
Why does one hop work? P(good path) = (1 – (1 -p)^2)^(R+1) R RON nodes 1 d( Ba ) -p source RON • • • In RON testbed: – P(direct path is good) is 48. 8% – P(intermediate path is good) is 51% RON Go o (p) d target
Resilience Against Do. S Attacks
Latency using RON
What’s next for RON? • Data mining of collected samples • Applications • Routing policies (e. g. , rate control)
Other progress: Chord • Chord: a peer-to-peer lookup system • CFS: a peer-to-peer file sharing application www. pdos. lcs. mit. edu/chord
Conclusion • Improved availability of Internet communication paths using small overlays – Layered above scalable IP substrate – RON provides a set of libraries and programs to facilitate this application-specific routing • Experimental data suggest that approach works – Over 10 X availability – Outage detection and recovery in about 15 seconds – Able to route around certain denial-of-service attacks • Many interesting questions remain… http: //nms. lcs. mit. edu/ron/
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