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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
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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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).
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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Background (BGP recap) Path vector protocol Incremental Updates Policy Enforcement Classless Inter-Domain Routing
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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.
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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.
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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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.
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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Distinction between BGP and HLP Design issueBGPHLP Routing structure FlatHierarchical Policy structureSupport for generic policies Optimize for common policies Granularity of routing Prefix basedAS based Style of routingPath vectorHybrid routing
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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.
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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.
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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HLP Routing Model Assumption: No cycles in Provider-Customer relationship
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HLP Routing Model
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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.
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HLP Routing Model (Cont.) Explicit Information Hiding
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HLP Protocol Model Prefix-level route selection. BGP uses prefix-deaggregate for traffic engineering. HLP uses information hiding.
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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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.
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HLP Protocol Analysis Churn reduction in HLP is due to a) using the AS-prefix mapping; b) cost hiding of route updates.
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HLP Protocol Analysis
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Roadmap Introduction Background Design Philosophy Distinctions between BGP and HLP HLP Routing Model HLP Protocol Analysis Conclusion
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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.
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