HLP: A Next Generation Interdomain Routing Protocol

HLP: A Next Generation Interdomain Routing Protocol Lakshminarayanan Subramanian, Matthew Caesar,Cheng Tien Ee, Mark Handley, Morley Mao, Scott Shenker,Ion Stoica To be appeared in SIGCOMM ‘05

Roadmap • Introduction • Background • Design Philosophy • Distinctions between BGP and HLP • HLP Routing Model • HLP Protocol Analysis • Conclusion

Introduction • BGP4 is the only inter-domain routing protocol in use. • Inter-domain routing protocol should satisfy basic properties, such as scalability, robustness ,rapid convergence and policy routing. • This paper describes a hybrid link-state and path vector protocol (HLP).

Background • (BGP recap) • Path vector protocol • Incremental Updates • Policy Enforcement • Classless Inter-Domain Routing

Background • (BGP Problems) • Route flapping -It is a propagation problem. • Security-BGP does not prevent an AS from advertising arbitrary prefixes • Peer scaling- Each must have a peer connection to every other router – creating a scaling problem as the number of connections increases exponentially with each new router added.

Background (Cont.) • BGP does not distribute policy information. • HLP expose the common case of policies. • Common and inferable relationship: Provider and customer relationship. • HLP leverages the common case policy behavior that BGP cannot hide and optimizes the protocol design.

Design Philosophy • Scalability: • 3000 ASs and 17,000 prefixes in 1997 • More than 50,000 ASs and 180,000 prefixes now • Convergence and Route Stability • Isolation: Isolate local faults within a network. • HLP Hide unnecessary routing updates across provider-customer hierarchies. • HLP does not use BGP’s prefix-deaggregation to do traffic engineering.

Distinction between BGP and HLP

Distinction between BGP and HLP (Cont.) • Routing structure - HLP avoids error propagation by hiding some path information using hierarchical routing structures. • Policy - 99% of the AS’s follow two simple guidelines. • Export-rule guideline: Do not forward route advertised by one peer or a provider to another peer or another peer or provider. • Route preference guideline: Prefer customer-routes advertised by peers or providers.

Distinction between BGP and HLP (Cont.) • Routing Granularity - Number of distinct paths from a vantage point to destination is less than 2 for more than 99%. • Routing Style- • PV- Worst case convergence grows exponentially with the length of the path • LS- Violates privacy of policies by revealing every activity to all destinations. • HLP uses LS within a given hierarchy and uses PV across hierarchies.

HLP Routing Model Assumption: No cycles in Provider-Customer relationship

HLP Routing Model

HLP Routing Model (Cont.) • (Summary) • All AS’s maintain a link-state database in their local hierarchy. • FPV includes peering links but excludes the parts within the hierarchies. • Cost metrics are added to the cost value in an FPV advertisement.

HLP Routing Model (Cont.) Explicit Information Hiding

HLP Protocol Model Prefix-level route selection. BGP uses prefix-deaggregate for traffic engineering. HLP uses information hiding.

HLP Protocol Analysis • (Quantification) • Isolation-The number of AS’s that can potentially be affected by a routing events. • Churn-The total number of updates generated by an event. • Topology: 16774 AS’s and 37066 inter-AS links.

HLP Protocol Analysis Churn reduction in HLP is due to a) using the AS-prefix mapping; b) cost hiding of route updates.

HLP Protocol Analysis

Conclusion • HLP performs better than BGP in isolation and churn reduction. • HLP converges faster and it provides a better security than BGP . • We shall wait and see whether BGP will be replaced or not since old habits are hard to die.

HLP: A Next Generation Interdomain Routing Protocol