Open shortest path first (OSPF) routing protocol simulation

ABSTRACT

Open Shortest Path First (OSPF) is a dynamic, hierarchical routing protocol designed to support routing in TCP/IP networks. A simulation of the OSPF Election Protocol shows three results: (1) The Designated Router (DR) can be elected in constant time. (2) If a router has a limited number of input buffers, a competition for buffers between the Election and the Flooding Protocols increases the election time and causes an oscillatory behavior.At each router, the Router-ID of the DR continuously changes causing instability. (3) In the worst case, when the DR and the BDR fail at the same time, the DR-agreement-time is bounded above by twice the HelloInterval. A simulation of the OSPF Flooding Protocol, using 20, 50 and 80 router point-to-point networks, shows three results: (1) For the 50 router network, as link speed exceeds 4000 Kbps, the probability of overflowing the input buffers increases causing retransmissions. The increase in bootup-convergence-time from retransmissions is bounded by two and three times the RxmtInterval for link speeds of 4000 to 6000 Kbps and above 50 Mbps respectively. The increase in the bootup-convergence-time is due to large number of unacknowledged flooding packets received within RxmtInterval. (2) For 20 and 50 router networks, the input buffer size has little impact on the bootup-convergence-time. For the 80 router network, a small change in the input buffer size drastically changes the bootup-convergence-time. (3) Reducing the value of the RxmtInterval lowers the bootup-convergence-time at high link speeds.

REFERENCES

• 1: j. Moy. The open shortest path first (OSPF) specification. Technical Report RFC-1131, SRI Network Information Center, October 1989.
• 2: Deepinder Sidhu, Tayang Fu, Shukri Abdallah, P~aj Nair, and Rob Coltun. Open shortest path first simulation, under preparation.

INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS
      C.2.2 Network Protocols

          Nouns: TCP/IP

Additional Classification:
  C. Computer Systems Organization
  C.2 COMPUTER-COMMUNICATION NETWORKS
      C.2.1 Network Architecture and Design
          Subjects: Network topology

  F. Theory of Computation
  F.2 ANALYSIS OF ALGORITHMS AND PROBLEM COMPLEXITY
      F.2.2 Nonnumerical Algorithms and Problems
          Subjects: Routing and layout

  G. Mathematics of Computing
  G.2 DISCRETE MATHEMATICS
      G.2.2 Graph Theory
          Subjects: Trees; Path and circuit problems

  I. Computing Methodologies
  I.6 SIMULATION AND MODELING
      I.6.8 Types of Simulation
          Subjects: Discrete event

General Terms:
Algorithms, Design, Performance, Reliability