slides.0419.2011

# slides.0419.2011 - In Byzantium Advanced Topics in...

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In Byzantium Advanced Topics in Distributed Systems Spring 2011 1

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Problem Computer systems provide crucial services Computer systems fail Crash-stop failure Crash-recovery failure Byzantine failure Example: natural disaster, malicious attack, hardware failure, software bug, etc. Why tolerate Byzantine fault? 2
Byzantine Generals Problem All loyal generals decide upon the same plan 3 Solvable if more than two-third of the generals are Attack Retreat Attack Attack/Retrea t Attack/Retrea t

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Byzantine Generals Problem 1: All loyal lieutenants obey the same order 2: If the commanding general is loyal, then every loyal lieutenant obeys the order he sends. General Lieutena nt Lieutena nt 4
Impossibility Results General Lieutena nt Lieutena nt Attack Attack Retreat 5

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Impossibility Results (2) General Lieutena nt Lieutena nt Attack Retreat Retreat No solution with fewer than 3m + 1 generals can cope with m traitors. 6
Lamport-Shostak-Pease Algorithm Algorithm OM(0) The general sends his value to every lieutenant. Each lieutenant uses the value he receives from the general. Algorithm OM(m), m>0 The general sends his value to each lieutenant. For each i , let vi be the value lieutenant i Stage 1: Messaging/Broadcasting Stage 2: Aggregation 7

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Stage 1: Broadcast Let, m = 2. Therefore, n = 3m + 1 = 7 Round 0: Generals sends order to all the lieutenants P1 P2 P4 P5 P3 P6 P7 0 0 0 1 1 1 <0, 1> <0, 1> <0, 1> <1, 1> <1, 1> <1, 1> 8
Stage 1: Round 1 P2 P4 P5 P3 P6 P7 <0, 12> <0, 12> <0, 12> <0, 12> <0, 12> <0, 12> <0, 13> <0, 13> <0, 13> <0, 13> <0, 13> <0, 13> <0, 14> <0, 14> <0, 14> <0, 14> <0, 14> <0, 14> <1, 15> <1, 15> <1, 15> <1, 15> <1, 15> <1, 16> <1, 16> <1, 16> <1, 16> <1, 16> <1, 17> <1, 17> <1, 17> <1, 17> <1, 17> <1, 15> <1, 16> <1, 17> 9

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Stage 1: Round 2 P4 P3 P5 P2 P6 P7 <0, 12> <0, 13> <0, 14> <1, 15> <1, 16> <1, 17> <0, 124> <0, 134> <0, 144> <1, 154> <1, 164> <1, 174> 4 says: in round 1, 2 told me that it received a ‘0’ from 1 in round 0. 10
Stage 2: Voting 11

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Stage 2: Voting (contd.) 12
Stage 2: Voting (contd.) 13

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Stage 2: Voting (contd.) 14
Practical Byzantine Fault Tolerance M. Castro and B. Liskov, OSDI 1999. Before PBFT: BFT was considered too impractical in practice Practical replication algorithm Reasonable performance Implementation BFT: A generic replication toolkit BFS: A replicated file system 15

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Challenges 16 Request A Request B Client Client
Challenges 17 2: Request B 1: Request A Client Client

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State Machine Replication 18 2: Request B 1: Request A 2: Request B 1: Request A 2: Request B 1: Request A 2: Request B 1: Request A Client Client How to assign sequence number to requests?
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## This note was uploaded on 12/08/2011 for the course CS 525 taught by Professor Gupta during the Spring '08 term at University of Illinois, Urbana Champaign.

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slides.0419.2011 - In Byzantium Advanced Topics in...

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