1. 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

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

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

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

14. 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

15. 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

16. 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

17. 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

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

19. HLP Protocol Analysis
50% globally visible.

20. HLP Protocol Analysis
Increasing multihomed links

21. HLP Protocol Analysis

22. 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

23. Q&A