HLP-A Next Generation Inter-Domain Routing Protocol Lakshminarayana Subramanian, Matthew Caesar, Cheng Tien Ee, Mark Handley, Morley Mao, Scott Shenker, Ion Stoica SIGCOMM 2005 Dec 6, 2006 Jaekyu Cho jkcho@mmlab.snu.ac.kr

Outline Introduction Basic Design Issues The HLP Routing Model Traffic Engineering Analysis Conclusion

Introduction Goals of Inter-Domain Routing AS2 AS1 AS3 Any inter-domain routing protocol should address three goals: ASs collectively achieve end-to-end routes consistent with policies An AS should not reveal its internal policies Desirable properties (scalability, convergence, isolation) AS1 AS4 AS5 AS3 AS2

Introduction An Exterior Gateway Protocol protocol used to pass routing information between two autonomous systems Border Gateway Protocol (BGP) a kind of exterior gateway protocol suppose AS to AS relation as flat structure Problem with BGP Scalability Convergence and Route Stability Isolation

Design Issues Distinctions between BGP and HLP Design Issue BGP HLP Routing Structure Flat Hierarchical Policy Structure Support for Generic Policies Optimize for common case Routing Granularity Prefix Based AS based Routing Style Path Vector Hybrid Routing

Design Issues Routing Structure Policy BGP reveals complete path information problem with scalability, isolation, localized security HLP hides some information using hierarchical structure Policy BGP keeps policy information private meaningless the relationship between ASs can be accurately inferred HLP explicitly publishes the provider-customer relationships restricts the normal set of available paths to a destination to those that obey the hierarchies defined by theses relationships

Design Issues Routing Granularity Routing Style BGP uses prefix-based routing route deaggregation for traffic engineering, multihoming and policy routing -> rising in the number of distinct prefixes in a routing tables HLP route at the granularity of AS’s instead of prefixes Routing Style BGP uses path-vector routing scalability, isolation, convergence problem HLP uses hybrid of link-state and path-vector link-state – fast convergence, low churn path-vector – global scalability by hiding internal route updates across hierarchy

HLP Routing Model HLP Routing Structure Path vector Tier-1 ASs Link State Path vector

HLP Routing Model Basic Route Propagation Model link-state routing within a provider-customer hierarchy granularity of AS’s every AS maintains link-state information path-vector routing across hierarchies similar to BGP fragmented path vector (FPV) exclude internal ASs information carries a cost metric

HLP Routing Model Example of Basic Route Propagation B A D C C F E D FPV[A,E] c=2 B LSA[C,E] c=1 FPV[B,A,E] c=3 D LSA[C,E] c=1 LSA[C,E] c=1 C C FPV[B,A,E] c=4 F E LSA[C,E] c=1 D

HLP Routing Model Example of Basic Route Propagation A B D C G F E H FPV[A,E] c=3 A B FPV[B,A,E] c=4 LSA[C,E] c=-1 LSA[C,E] c=-1 D LSA[C,E] c=-1 C G FPV[B,A,E] c=5 F E H

HLP Routing Model Explicit information hiding using costs propagate a route update only when necessary Use cost-threshold defined by the AS Three forms of cost-hiding not propagating minor cost changes of customer routes not propagating minor cost changes of peer routes hiding failure of one of multiple parallel peering links between a pair of AS’s

HLP Routing Model Explicit information hiding using costs B A No update B (E,D) Link Failure E C D

HLP Routing Model Explicit information hiding using costs D unreachable X A Y No update No update B C F E (E,D) Link Failure D

Traffic Engineering BGP was never designed to do TE HLP can support TE While maintaining the basic scalability, isolation and convergence advantage Traffic engineering mechanism AS’s the flexibility to perform prefix-level route selection AS’s the ability to achieve inbound traffic engineering by manipulating link-costs

Traffic Engineering Prefix-level route Selection HLP uses information hiding to support prefix-level route selection B D E A C No update Path P1 Path P2 X Y F

Traffic Engineering Cost-based inbound traffic engineering BGP uses AS prepending HLP: Each AS can manipulate the cost of its inter-AS links to achieve volume based inbound Traffic Engineering A B C M Choice Route Destination Networks a b c

HLP Protocol Analysis About 80% of the events create more than 10000 churns On the other side,

HLP Protocol Analysis 50% globally visible.

HLP Protocol Analysis Increasing multihomed links

HLP Protocol Analysis

Conclusion There is a definite need to revisit the design of inter-domain routing How long can BGP adapt to Internet growth is questionable? Incremental fixes to BGP may not suffice for the long-term HLP is one point in the design space HLP does not modify the operational model of BGP (concept of ASs, relationships remain) HLP improves scalability, isolation and convergence

Q&A