Contra: A Programmable System for Performance aware Routing
summary
System compiles high-level path-ranking policies into switch-local P4 programs and a product graph that merges regex path constraints with the topology. Runtime uses compact, sequence-numbered probes that carry path metrics and a distance‑vector style update to install best paths, plus policy-aware flowlet pinning to avoid reordering and policy violations. Prototype compiles policies in seconds, runs entirely in the data plane, matches hand‑tuned Hula on fat trees, scales to large topologies, and sees only rare transient loops.
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chapters (15)
- 0:00Intro
- 0:17Motivation: Performance-aware routing
- 4:21Contra language syntax
- 4:37Contra can support many policies
- 5:23How can we compile the policies to switch programs?
- 5:57Policy analysis
- 6:39Defining routing protocols on the PG
- 9:48Handling changing metrics: Loops
- 11:05Handling changing metrics: Out-of-order delivery
- 11:47Handling change metrics: Policy violation by flowers
- 13:23Evaluation setup
- 13:41How scalable is the Contra compiler?
- 14:14How competitive is contra against hand-crafted solutions?
- 15:19How about arbitrary topologies?
- 17:07Conclusion
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