Transcript Exploiting Route Redundancy via Structured Peer to Peer Overlays

Exploiting Route Redundancy via
Structured Peer to Peer Overlays
Ben Y. Zhao, Ling Huang, Jeremy Stribling,
Anthony D. Joseph, and John D. Kubiatowicz
University of California, Berkeley
ICNP 2003
Challenges Facing Network Applications
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Network connectivity is not reliable
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Disconnections frequent in the wide-area Internet
IP-level repair is slow
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Wide-area: BGP  3 mins
Local-area: IS-IS  5 seconds
Next generation network applications
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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
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Motivation
Why structured routing
Structured Peer to Peer overlays
Mechanisms and policy
Evaluation
Summary
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Routing in “Mesh-like” Networks
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Previous work has shown reasons for long
convergence [Labovitz00, Labovitz01]
MinRouteAdver timer
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Necessary to aggregate updates from all neighbors
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Contributes to lower bound of BGP convergence time
Internet becoming more mesh-like [Kaat99,labovitz99]
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Commonly set to 30 seconds
Worsens BGP convergence behavior
Question
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Can convergence be faster in context of structured routing?
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Resilient Overlay Networks (MIT)
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Fully connected mesh
Allows each node full
knowledge of network
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D
Fast, independent calculation
of routes
Nodes can construct any
path, maximum flexibility
Cost of flexibility
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Protocol needs to choose the
“right” route/nodes
Per node O(n) state
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Monitors n - 1 paths
O(n2) total path monitoring is
expensive
S
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Leveraging Structured Peer-to-Peer Overlays
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0
Key based routing (IPTPS 03)
 Large sparse ID space N
root(k)
(160 bits: 0 – 2160)
 Nodes in overlay network
have nodeIDs  N
 Given some key k  N,
overlay deterministically
maps k to its root node (live
node in the network)
 route message to root (k)
source
k
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Distributed Hashtables (DHT) is interface on KBR
 Key is leveraging underlying routing mesh
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Proximity Neighbor Selection
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PNS = network aware overlay construction
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Important for routing
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Within routing constraints, choose neighbors closest in
network distance (latency)
Generally reduces # of IP hops
Reduce latency
Reduce susceptibility to faults
 Less IP links = smaller chance of link/router failure
Reduce overall network bandwidth utilization
We use Tapestry to demonstrate our design
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P2P protocol with PNS overlay construction
Topology-unaware P2P protocols will likely perform worse
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System Architecture
v
v
v
v
v
v
OVERLAY
v
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v
Internet
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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 A
P’(B)
B
Legacy
Node B
register
register
Proxy
P’(A) = A
P’(B) = B
Proxy
get (hash(B)) P’(B)
put (hash(A), P’(A))
put (hash(B), P’(B))
Structured Peer to
Peer Overlay
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Store mapping from end host IP to its proxy’s overlay ID
Similar to approach in Internet Indirection Infrastructure (I3)
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Tradeoffs of Tunneling via P2P
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Less neighbor paths to monitor per node: O(log(n))
 Large reduction in probing bandwidth: O(n)  O(log(n))
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Actively maintain path redundancy
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Manageable for “small” # of paths
Redirect traffic immediately when a failure is detected
Eliminate on-the-fly calculation of new routes
Restore redundancy when a path fails
End result
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Increase probing frequency
Faster fault detection with low bandwidth consumption
Fast fault detection + precomputed paths = increased
responsiveness to faults
Cons
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Overlay imposes routing stretch (more IP hops), generally < 2
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Some Details
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Efficient fault detection
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Use soft-state to periodically probe log(n) neighbor paths
“Small” number of routes  reduced bandwidth
Exponentially weighted moving average
in link quality estimation
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Avoid route flapping due to short term loss artifacts
Loss rate Ln = (1 - )  Ln-1 +   p
p = instantaneous loss rate,  = hysteresis factor
Maintaining backup paths
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Each hop has flexible routing constraint
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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)
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Use estimated loss results to
choose shortest “usable” path
Sort next hop paths by latency
Use shortest path with
2299
minimal quality > T
Correlated failures
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Reduce with intelligent topology
construction
Key is to leverage redundancy
available
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2225
2274
2046
2286
2281
2530
1111
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Evaluation
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Metrics for evaluation
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How much routing resiliency can we exploit?
How fast can we adapt to faults?
What is the overhead of routing around a failure?
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Proportional increase in end to end latency
Proportional increase in end to end bandwidth used
Experimental platforms
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Event-based simulations on transit stub topologies
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Data collected over different 5000-node topologies
PlanetLab measurements
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Microbenchmarks on responsiveness
Bandwidth measurements from 200+ node overlays
Multiple virtual nodes run per physical machine
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% of All Pairs Reachable
Exploiting Route Redundancy (Sim)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Instantaneous IP
0
0.05
Tapestry / FRLS
0.1
0.15
0.2
Proportion of IP Links Broken
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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)
Time to Switch Routes (ms)
2500
2000
1500
1000
660
alpha=0.2
alpha=0.4
500
0
0
200
300
400
600
800
1000
1200
Link Probe Period (ms)
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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)
Bandwidth Per Node (KB/s)
7
PR=300ms
PR=600ms
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5
4
3
2
1
0
1
10
100
1000
Size of Overlay
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Medium sized routing overlays incur low probing bandwidth
Bandwidth increases logarithmically with overlay size
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Related Work
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Redirection overlays
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Topology estimation techniques
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Detour (IEEE Micro 99)
Resilient Overlay Networks (SOSP 01)
Internet Indirection Infrastructure (SIGCOMM 02)
Secure Overlay Services (SIGCOMM 02)
Adaptive probing (IPTPS 03)
Peer-based shared estimation (Zhuang 03)
Internet tomography (Chen 03)
Routing underlay (SIGCOMM 03)
Structured peer-to-peer overlays
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Tapestry, Pastry, Chord, CAN, Kademlia, Skipnet, Viceroy,
Symphony, Koorde, Bamboo, X-Ring…
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Conclusion
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Benefits of structure outweigh costs
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Structured routing lowers path maintenance costs
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Can no longer construct arbitrary paths
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Structured routing with low redundancy gets very close to ideal in
connectivity
Incur low routing stretch
Fast enough for highly interactive applications
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Allows “caching” of backup paths for quick failover
300ms beacon period  response time < 700ms
On overlay networks of 300 nodes, b/w cost is 7KB/s
Future work
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Deploying a public routing and proxy service on PlanetLab
Examine impact of
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Network aware topology construction
Loss sensitive probing techniques
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Questions…
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Related websites:
Tapestry
http://www.cs.berkeley.edu/~ravenben/tapestry
 Pastry
http://research.microsoft.com/~antr/pastry
 Chord
http://lcs.mit.edu/chord
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Acknowledgements
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Thanks to Dennis Geels and Sean Rhea for their
work on the BMark benchmark suite
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Backup Slides
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Another Perspective on Reachability
Proportion of All Paths
1
0.9
0.8
Portion of all pairwise paths where
no failure-free
paths remain
0.7
A path exists, but
neither IP nor
FRLS can locate
the path
0.6
0.5
0.4
0.3
0.2
0.1
Portion of0 all paths
where IP0 and
FRLS both route
successfully
November 7, 2003
0.05
0.1
0.15
Proportion of IP Links Broken
ICNP 2003
FRLS finds
path, 0.2
where
short-term IP
routing fails
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Constrained Multicast
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Used only when all paths are below
quality threshold
Send duplicate messages on multiple
paths
Leverage route convergence
2299
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 Assign unique message
IDs
 Mark duplicates
 Keep moving window of IDs
2046
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 Recognize and drop duplicates
? ? ?
Limitations
 Assumes loss not from congestion
1111
 Ideal for local area routing
November 7, 2003
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2225
2286
2530
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Latency Overhead of Misrouting
Proportional Latency Overhead
Hop 0
Hop 1
Hop 4
Hop 3
Hop 2
1
0.9
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0.5
0.4
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0.2
0.1
0
20
40
60
80
100
120
160
140
180
Latency from source to destination (ms)
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Bandwidth Cost of Constrained Multicast
Proportional Bandwidth Overhead
Hop 0
Hop 1
Hop 2
Hop 3
Hop 4
1
0.9
0.8
0.7
0.6
0.5
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0.2
0.1
0
20
40
60
80
100
120
140
160
Latency from source to destination (ms)
November 7, 2003
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Challenge 2: Tunneling Application Traffic
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Basic idea
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Desired properties
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Tunnel “legacy” traffic via overlay proxies
Should be protocol independent
Traffic redirection transparent to end hosts
Stable mapping between a proxy and its legacy nodes
Incremental deployment
Details
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Making a connection to D
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Determine if D is reachable from overlay
If so, retrieve D’s overlay ID from storage in overlay
Redirect traffic through overlay to D’s overlay ID
Assign legacy nodes IDs in the overlay
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Routing to IDs automatically reach respective proxies
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Assigning Overlay Identifiers
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A proxy close by in network
assigns a legacy node a
non-random overlay ID
Assign closest possible
ID to proxy’s ID
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proxy
proxy
source
node ID
such that: root (ID) = proxy
Chord/Tapestry: ID = proxyID – 1
Stable ID mapping
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Probability of a new node
“hijacking” legacy node very low
1 million nodes,
1000 nodes / proxy,
160 bit names, Ph < 10-40
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destination
node ID
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Unused Slides
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Summary
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Highly adaptive to link failures
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Fast adaptation time w/ low monitoring BW cost
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300ms beacon period, 7KB/s (300 overlay nodes),
response time < 700ms
Low latency and BW overhead for misrouting
Limitation: less useful for congested IP links
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Constrained multicast can exacerbate congestion
Can utilize more physically-aware overlay construction
Issue: using loss as congestion indicator
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Can fix with more intelligent protocols such as XCP
November 7, 2003
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Possible Approaches
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Modify basic IP protocols
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“Helper” infrastructures to assist protocols
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BGP, OSPF, IS-IS
Millions of deployed routers  Significant
deployment challenge
Manipulate input to improve performance without
modification
Deploy intelligent protocols above IP layer
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Overlay approach taken by many
Relies on basic point to point IP routing
November 7, 2003
ICNP 2003
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