Gagan Choudhury AT&T gchoudhury@att

1. LSA Flooding Optimization Algorithms and Their Simulation Study (draft-choudhury-manral-flooding-simulation-00.txt) Gagan Choudhury AT&T gchoudhury@att.com Vishwas Manral NetPlane Systems VishwasM@netplane.com

2. The Basic Issue • Flooding Over All Interfaces is Highly Reliable But in Large Networks it May Cause Sustained CPU Congestion (Often Memory Congestion as well) During LSA Storms Triggered By • Links/Nodes Failures • Synchronization of Refreshes • Software Bugs or Procedural Errors • Congestion Reinforced by Positive Feedback Loop due to • LSA Retransmissions, possible packet droppings, possible link failures due to missed Hellos and eventual recoveries More LSAs • On Rare Occasions the Congestion Spreads to Many Nodes and Cause Significant Failures (Observed in Operational Networks) • We Show Simulation Study on How Stability/Scalability of Networks May Be Improved with Restrictive Flooding Algorithms and Propose that a Subset of These Schemes be Pursued Further

3. Flooding Algorithms • Algorithm 1: Flood over All Interfaces (Existing Algorithm) • Algorithm 2: Full Flooding But Flood over Only one of Many Parallel Links Between Neighbors (Zinin/Shand ID, Moy ID, Used in PNNI) • Algorithm 3: Algorithm 2 + Full Flooding only at Multipoint Relays Chosen by Each Node Independently • Algorithm 4: Algorithm 2 + Flooding only Along a Minimum Spanning Tree (If a Link Along the Tree Fails the MST Needs to be Re-computed): Not Robust Under Failures • Algorithm 5: Algorithm 2 for LSAs Carrying Intra-Area Topology (Router, Network), Algorithm 4 for Other LSAs (ASE, TE, Summary) • Modified Algorithm 5: Flooding Links Survivable Under Single Link and Single Node Failures (Results Not Reported)

4. Alternate Simulation Scenarios • Network Scenarios: • Network 1: 100 Nodes, 1200 Links, Max Neighbors 30, Max Node Adjacency 50 • Network 2: 50 Nodes, 600 Links, Max Neighbors 25, Max Node Adjacency 48 • LSA Scenarios • 1 Router LSA per Node, 1 TE LSA per Link • 1 Router LSA per Node, 10 ASE LSAs per Every Other Node • LSU Processing Time : ~ 1 ms, ~0.5 ms, ~2 ms

5. Five Simulation Cases • Case 1: Network 1, Link LSAs, Proc. Time ~ 1 ms • Case 2: Network 1, ASE LSAs, Proc. Time ~ 1 ms • Case 3: Network 1, Link LSAs, Proc. Time ~ 0.5 ms • Case 4: Network 1, Link LSAs, Proc. Time ~ 2 ms • Case 5: Network 2, Link LSAs, Proc. Time ~ 1 ms

6. Number of Non-Converged LSAs Vs. LSA Storm - Case 1, Algorithm 1 - LSA Storm Starts Between 20 and 30 Seconds

7. LSA Storm Threshold for Sustained CPU Congestion

8. Observations on Flooding Algorithms • Flooding Over one of Many Parallel Links (Alg. 2) May Significantly Improve Scalability over Current Algorithm (Alg. 1) • Zinin/Shand ID/ Moy ID Should be Pursued Further • Further Restriction With MPR (Alg 3) Has Moderate Improvement • Neighbors of High Adjacency Node Tend to Declare it as MPR • Flooding Only Over Minimum Spanning Tree (Alg 4) Greatly Improves Scalability But Not Robust Under Failure • Full Flooding for LSAs Carrying Intra-Area Topology and MST Flooding for Others (Alg 5) May Be Almost As Scalable as Alg 4 But Also More Robust • Modification to Alg 5 with Disjoint MSTs + Other Flooding Links to Ensure Robustness Under Single Link and Single Node Failures Have Been Considered (Not Reported) • Quite Robust and Significantly More Scalable Compared to Alg 2 • Alg 2, Alg 5 and Modified Alg 5 Should Be Pursued Further