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).

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

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.

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

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 p

rovider-customer hierarchies.• HLP does not use BGP’s prefix-deaggregation to

do traffic engineering.

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

Distinction between BGP and HLPDesign issue BGP HLP

Routing structure

Flat Hierarchical

Policy structure Support for generic policies

Optimize for common policies

Granularity of routing

Prefix based AS based

Style of routing Path vector Hybrid routing

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.

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

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 ModelPrefix-level route selection.

BGP uses prefix-deaggregate for traffic engineering.

HLP uses information hiding.

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

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

HLP Protocol Analysis

HLP Protocol Analysis

HLP Protocol Analysis

Roadmap

• Introduction

• Background

• Design Philosophy

• Distinctions between BGP and HLP

• HLP Routing Model

• HLP Protocol Analysis

• Conclusion

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.