Infrastructurebased Resilient Routing

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Infrastructure-basedResilient Routing

• Ben Y. Zhao, Ling Huang, Jeremy Stribling,
  Anthony Joseph and John Kubiatowicz
• University of California, Berkeley
• Sahara Winter Retreat, 2004

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Challenges Facing Network Applications

• Network connectivity is not reliable
• Disconnections frequent in the wide-area Internet
• IP-level repair is slow
• Wide-area BGP ? 3 mins
• Local-area IS-IS ? 5 seconds
• Next generation network applications
• Mostly wide-area
• Streaming media, VoIP, B2B transactions
• Low tolerance of delay, jitter and faults
• Our work transparent resilient routing
  infrastructure that adapts to faults in not
  seconds, but milliseconds

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Talk Overview

• Motivation
• A Structured Overlay Infrastructure
• Mechanisms and policy
• Evaluation
• Summary

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The Challenge

• Routing failures are diverse
• Many causes
• Router misconfigurations, cut fiber, planned
  downtime, protocol implementation bugs
• Occur anywhere with local or global impact
• Single fiber cut can disconnect AS pairs
• Isolating failures is difficult
• Wide-area measurement is ongoing research
• Single event leads to complex inter-protocol
  interactions
• End user symptoms often dynamic or intermittent
• Requires
• Fault detection from multiple distributed vantage
  points
• In-network decision making necessary for timely
  responses

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An Infrastructure Approach

• Our goals
• Overlay focused on resiliency
• Route around failures to maintain connectivity
• Respond in milliseconds (react instantaneously to
  faults)
• Our approach
• Large-scale infrastructure for fault and route
  discovery
• Nodes are observation points (similar to Platos
  NEWS service)
• Nodes are also points of traffic
  redirection(forwarding path determination and
  data forwarding)
• Automated fault-detection and circumvention
• No edge node involvement fast response time,
  security focused on infrastructure
• Fully transparent, no application awareness
  necessary

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An Illustration
Goal fast fault detection and route-around
Key on the fly in-network traffic redirection
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Why Structured Overlays

• Resilient Overlay Networks (MIT)
• Fully connected mesh
• Allows each node full knowledge of network
• Fast, independent calculation of routes
• Nodes can construct any path, maximum flexibility
• Cost of flexibility
• Protocol needs to choose the right route/nodes
• Per node O(n) state
• Monitors n - 1 paths
• O(n2) total path monitoring is expensive

D
S
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The Big Picture
Internet

• Locate nearby overlay proxy
• Establish overlay path to destination host
• Overlay traffic routes traffic resiliently

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Traffic Tunneling
A, B are IP addresses
Legacy Node B
Legacy Node A
B
P(B)
Proxy
P(B) B
P(A) A
Proxy
Structured Peer to Peer Overlay

• Store mapping from end host IP to its proxys
  overlay ID
• Similar to approach in Internet Indirection
  Infrastructure (I3)

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Tradeoffs of Tunneling via P2P

• Less neighbor paths to monitor per node
  O(log(n))
• Large reduction in probing bandwidth O(n) ?
  O(log(n))
• Faster fault detection with low bandwidth
  consumption
• Actively maintain path redundancy
• Manageable for small of paths
• Redirect traffic immediately when a failure is
  detectedEliminate on-the-fly calculation of new
  routes
• Restore redundancy when a path fails
• Fast fault detection precomputed paths
  increased responsiveness
• Cons overlay imposes routing stretch (mostly lt 2)

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In-network Resiliency Mechanisms

• Efficient fault detection
• Use soft-state to periodically probe log(n)
  neighbor paths
• Small number of routes ? reduced bandwidth
• Exponentially weighted moving averagefor link
  quality estimation
• Avoid route flapping due to short term loss
  artifacts
• Loss rate Ln (1 - ?) ? Ln-1 ? ? ?p
• Simple approach taken, ongoing research available
• Smart fault-detection / propagation (Zhuang04)
• Intelligent and cooperative path selection
  (Seshardri04)
• Maintaining backup paths
• Each hop has flexible routing constraint
• Create and store backup routes at node insertion
• Restore redundancy via intelligent gossip after
  failures
• Simple policies to choose among redundant paths

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First Reachable Link Selection (FRLS)

• Use estimated loss results to choose shortest
  usable path
• Sort next hop paths by latency
• Use shortest path withminimal quality gt T
• Correlated failures
• Reduce with intelligent topology construction
• Key is to leverage redundancy available

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Evaluation

• Metrics for evaluation
• How much routing resiliency can we exploit?
• How fast can we adapt to faults (responsiveness)?
• Experimental platforms
• Event-based simulations on transit stub
  topologies
• Data collected over multiple 5000-node topologies
• PlanetLab measurements
• Microbenchmarks on responsiveness
• More details in paper (ICNP03) and poster session

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Exploiting Route Redundancy (Sim)

• Simulation of Tapestry, 2 backup paths per
  routing entry
• Transit-stub topology shown, results from TIER
  and AS graphs similar

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Responsiveness to Faults (PlanetLab)

• Response time increases linearly with probe
  period
• Minimum link quality threshold T 70, 20 runs
  per data point

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Link Probing Bandwidth (Planetlab)

• Medium sized routing overlays incur low probing
  bandwidth
• Bandwidth increases logarithmically with overlay
  size

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Conclusion

• Pros and cons of infrastructure approach
• Structured routing has low path maintenance costs
• Allows caching of backup paths for quick
  failover
• Transparent to user applications
• Can no longer construct arbitrary paths
• Structured routing with low redundancy close to
  ideal connectivity
• Incur low routing stretch
• Fast enough for highly interactive applications
• 300ms beacon period ? response time lt 700ms
• On overlay networks of 300 nodes, b/w cost is
  7KB/s
• Ongoing questions
• Is there lower bound on desired
  responsiveness?Should we use multipath redundant
  routing for resilience?
• How to deploy as a single network across
  ISPs?VPN-like routing service?

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Related Work

• Redirection overlays
• Detour (IEEE Micro 99)
• Resilient Overlay Networks (SOSP 01)
• Internet Indirection Infrastructure (SIGCOMM 02)
• Secure Overlay Services (SIGCOMM 02)
• Topology estimation techniques
• Adaptive probing (IPTPS 03)
• Internet tomography (IMC 03)
• Routing underlay (SIGCOMM 03)
• Many, many other structured peer-to-peer
  overlays
• Thanks to Dennis Geels / Sean Rhea for their work
  on BMark