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Formal Verification of AODV Protocol using Cadence SMV

Formal Verification of AODV Protocol using Cadence SMV. (CPSC513 Course Project). Xin Liu and Jun Wang liu@cs.ubc.ca , jwang@cs.ubc.ca. Outline. Motivation AODV Introduction Building Model Conclusion. Motivation.

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Formal Verification of AODV Protocol using Cadence SMV

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  1. Formal Verification of AODV Protocolusing Cadence SMV (CPSC513 Course Project) Xin Liu and Jun Wang liu@cs.ubc.ca, jwang@cs.ubc.ca

  2. Outline • Motivation • AODV Introduction • Building Model • Conclusion

  3. Motivation • Find an appropriate approach to use Cadence SMV verifying real-life software communication protocols, such as AODV. The emphasis is on how to build the model. • Find some bugs in AODV protocol (RFC3561)? Hope we can…

  4. AODV Introduction • AODV (Ad hoc On-demand Distance Vector) Protocol • a reactive routing protocol for ad hoc mobile networks. • IETF standardizing for MANET. • 13 Internet drafts, 1 experimental RFC3561 (July 2003) • Important property: Loop free

  5. AODV Introduction (cont.) • Example: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 0 RREQ: - RREQ: - RREP: 0, 0 B intermediator

  6. AODV Introduction (cont.) • Example: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 0 RREP: 0, 1 B intermediator

  7. AODV Introduction (cont.) • Example: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 0 B intermediator

  8. Building Model • We have built 4 versions of models. • Some tricks in modeling:(included in all the models) • How to model node: we do not model node as a module, instead, we model each operation of nodes as a module, such as route discovery, receive a RREP, etc. • Timeout: nondeterminism or counter. • Sequence Number: it’s too expensive to model it as infinite or 32 bits long. Solution is using small number (<3) and a boundary value. • Periodical Hello message: it’s very hard to model periodical message in SMV, so the solution is not to model it directly. Instead, we model link break as a process, which has the same effect as not receiving periodical hello message. • Message Loss: easy to model, but hard to be fair. Solution is to use fairness constraints if the property we are verifying is reachability. For Loop-free property, nondeterminism is fine.

  9. Building Model – 1st Model • 1st Model(Naïve approach): • Try to build a complete and general model. • Results: • 2 nodes model can work, but it consumes 300 ~ 400 MB memory. • 3 nodes model state explosion! 

  10. Building Model – 2nd Model • 2nd Model: • Every node has a specific role: originator, intermediator, or destination. Only originator can initiate route discovery. Each node only maintains data which is related to its role. • Enumerate possible network topology, model separately for each meaningful topology.

  11. Building Model – 2nd Model • 3 nodespossible network topology: originator originator intermediator destination (a) Linear Topology destination intermediator (b) Triangle Topology

  12. Building Model – 2nd Model • Result: • The result is “Great!”, we found 2 “bugs”, one is found by Linear model, the other is found by Triangle model. • Table • Are they really bugs? • No, we found that we increased destination sequence number incorrectly in some situation.  • We should be more careful to model the protocol, but we think that RFC3561 is not organized very well, and it is not written clearly.

  13. Building Model – 3rd Model • 3rd Model: • First, fix the mistakes in the 2nd Model. • Minimize the number of variables further. We get rid of the variables which can be derived by other variables. • Besides considering 3 nodes, also consider 4 nodes possible network topology, model the meaningful topology separately.

  14. Building Model – 3rd Model • 4 nodespossible network topology: Star Topology Umbrella Topology Linear Topology Diamond Topology Camel Topology Complete Topology

  15. Building Model – 3rd Model • We modeled the star and umbrella topology for 4 nodes. • Result: • 3 nodes models can work. • 4 nodes star topology can work, it has 98 variables, consumes 45 MB memory, and runs for 2 minutes. • But 4 nodes umbrella topology can not work, it does not state explosion, instead, whenever it consumes 600+MB memory, SMV crash!  • The verification result: • “Loop free”

  16. Building Model – 4th Model • Is AODV really loop free? What else can we do? • During model construction, we did abstractions, lots of details are not considered and modeled. • Look at RFC3561 more carefully, we found this sentence: “A node initiates a RERR message in three situations: (i)… (ii) if it gets a data packet destined to a node for which it does not have an active route… (iii)…” • We decide to add the data packet into our model.

  17. Building Model – 4th Model • 4th Model: • Add the data packet into the model. • Results: • 3 nodes triangle model found a bug, Great!!! • We double checked the RFC3561, we think that it is a real bug! 

  18. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 0 RREQ: 1 (loss) X Link break Repair B intermediator

  19. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 0 X Link break RERR: 0 (loss) Repair timeout B intermediator

  20. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator RREQ: 1 A C destination Seq: 0 RREQ: 1 X Link break B intermediator

  21. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator RREP: 1, 0 A C destination Seq: 1 Data packet X Link break B intermediator

  22. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 1 RREP: 1, 1 X Link break RERR: 1 B intermediator

  23. Building Model – 4th Model • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A C destination Seq: 1 X Link break B intermediator

  24. Building Model – 4th Model • The bug we found: • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A X Link break C destination Seq: 1 RREQ: 1 X Link break RREP: 1, 2 B intermediator

  25. Building Model – 4th Model • The bug we found: • The bug we found: RREQ: dest_seq RREP: dest_seq, hop_count RERR: dest_seq originator A X Link break C destination Seq: 1 X Link break B intermediator

  26. Conclusion • We find an appropriate approach to use SMV verifying AODV protocol, that is, model separately for each role and for each possible network topology. • We find a bug in current AODV protocol. • We think SMV is not a suitable tools for verifying communication protocols, it is more suitable for verifying hardware systems. • To verify real-life communication protocols, you need a very powerful machine, our suggestion is try to find a Mainframe…

  27. References • RFC3561http://www.faqs.org/rfcs/rfc3561.html • Cadence SMV documentation • K. Bhargavan, D. Obradovic, C. A. Gunter, Formal Verification of Standards for Distance Vector Routing Protocols, JACM, Volume 49 , Issue 4, July 2002. • Sibusisiwe Chiyangwa, Marta Kwiatkowska, Modeling Ad hoc On-demand Distance Vector (AODV) Protocol with Time Automata, inProc, Third Workshop on Automated verification of Critical Systems (AVoCS'03), Southampton April 2003 • …

  28. Formal Verification of AODV Protocol using Cadence SMV Thanks! Created by Xin Liu and Jun Wang, April 3, 2004

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