Impact of Neighbor Selection on Performance and Resilience of Structured P2P Networks IPTPS Feb. 25, 2005 Byung-Gon Chun, Ben Y. Zhao, and John Kubiatowicz UC Berkeley and UC Santa Barbara

Structured P2P Overlay 00… 01…10… 11… Source Destination Berkeley MIT

Unbalanced Overlay Structure CDF of node degrees of a 205-node Bamboo overlay running on PlanetLab

Talk Outline Motivation –Impact of neighbor selection on resilience Neighbor selection model Simulation setup Performance Static resilience Redundancy

Routing Details Chord (ring geometry) –Each node forwards to the live neighbor that is closest to the destination in the identifier space –The lookup fails if all neighbors before the destination in the identifier space fail Tapestry (tree geometry) –Each node forwards messages to the first live neighbor matching one more prefix digit –The lookup fails, if all primary and backup links in the routing entry fail

Neighbor Selection Model Neighbor selection is a cost minimization problem pathcost(src,dst) = edgecost(src,nbr) + nodecost(nbr) + remaining_pathcost(nbr, dst) edgecost: network latency, nodecost: processing delay

Neighbor Selection Model ModelCost of node i RandomN/A Dist (PNS)∑edgecost(i,nbr) Cap∑nodecost(nbr) CapDist∑[edgecost(i,nbr) + nodecost(nbr)]

Simulation Setup A neighbor is chosen among 32 sample nodes 5100 node transit-stub physical networks 4096 overlay nodes at random physical locations 3 topologies and 3 overlay node placements Node capacity model –Coarse-grained uniform distribution : pick a processing delay randomly among (  /10, 2  /10,..,  ) where  is the maximum processing delay in seconds –Bimodal distribution (fast and slow nodes)

Performance under Uniform Processing Delay Distribution

Failure and Attack Model Random node failures –Choose a fraction of nodes randomly Targeted node attacks –Sort nodes with in-degree, remove nodes with high in-degree first Resilience metric –Failed paths: proportion of all pairs of live nodes that cannot route to each other via the overlay after a failure or attack event

Random Node Failures Tapestry (tree)Chord (ring)

Targeted Node Attacks Chord (ring)Tapestry (tree)

Redundancy (Random links) Backup links Sequential neighbors

Hybrid Achieves Resilience against Targeted Attacks Chord (12 sequential neighbors)Tapestry (2 random backup links)

Related Work Gummadi et al. (SIGCOMM 2003) –Routing geometry –PNS, PRS –Random node failures Castro et al. (OSDI 2002) –Eclipse attacks - fake proximity –Two routing tables: proximity-based and constrained Singh et al. (SIGOPS EW 2004) –Node degree bounding Albert, Jeong, and Barabasi (Nature, 2000) –Power-law graph Chun et al. (INFOCOM 2004) –Selfishly constructed overlay

Conclusion Neighbor selections that consider network proximity and node capacity improve routing performance Such neighbor selections do not affect resilience against random failures These performance benefits come with loss in attack tolerance Adding redundancy (w. randomness) can shield against targeted attacks

Impact of Neighbor Selection on Performance and Resilience of Structured P2P Networks IPTPS Feb. 25, 2005 Byung-Gon Chun, Ben Y. Zhao, and John Kubiatowicz UC Berkeley, UC Santa Barbara