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Inter-Domain Routing: Stability, Policies, and Incentives

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Inter-Domain Routing:

Stability, Policies, and Incentives

Vijay Ramachandran

http://www.icsi.berkeley.edu/~vijayr

Supported by the DoD URI program

under ONR grant N00014-01-1-0795

(2)

Overview of Results:

Two SPYCE-Sponsored Collaborations



Aaron Jaggard

- Framework for design and analysis of inter-domain routing protocols

- Expanded to include more complex policies



Joan Feigenbaum and Michael Schapira

- New class of policies for BGP-based, incentive-compatible routing; partially answers goal for option period

NEW NEW

(3)

Inter-Domain Routing

Establish routes between autonomous systems (ASes).

Currently done with the Border Gateway Protocol (BGP).

AT&T

Qwest

Comcast UUNET

(4)

Why is Inter-Domain Routing Hard?

 Route choices are based on local policies.

 Autonomy: Policies are uncoordinated.

 Expressiveness: Policies are complex.

AT&T

Qwest

Comcast UUNET

My link to UUNET is for backup purposes only. Load-balance my outgoing traffic. Always choose shortest paths. Avoid routes through AT&T if at all possible.

(5)

Three Desiderata

Incentive Compatibility Backward Compatibility Realistic Routing Model

Can get 2 out of 3

2 are SPYCE achievements

Open question for option: Can we satisfy all 3?

BGP Po licy Ro uting Lowest-Cost Routing

(6)

Yes!

 Next-hop routing with today’s

Internet business relationships.

 Optimal routing tree given

nodes’ valuations; incentivize nodes to report truthful

valuations using VCG payments.

 Compute routes and payments in

a BGP-compatible way. Incentive Compatibility Backward Compatibility Realistic Routing Model

(7)

BGP Route Processing

 Pros:

- Route choices depend on neighbors’ choices. => enforces consistency

- Best-route choices are made locally. => allows autonomy & expressiveness.

- Routes are loop free and can change with topology, without any node’s knowing the whole network.

 Cons:

- Policy-induced routing anomalies => Routes may not be stable.

Receive routes from neighbors Store routes Choose “best” route Send updates to neighbors

(8)

SPYCE Contributions:

Policy Constraints for Stability

Local constraint (equivalent to per-path lowest-cost routing) No global constraint Stability No Expressiveness No Autonomy

+

Policies compatible with generalizations of Internet hierarchy Global constraint Stability Expressiveness Autonomy

+

Generation algorithm Enforcement algorithms (centralized or distributed) or

(9)

Expanding the Model

Update Messages P1 P2 P3 Import Policy rank1 rank2 rank3 Route Selection rank2 is lowest => choose P2 P2 Export Update Messages P1 P2 P3

Generalized Route Selection

P2 Export P1 P2 P3 P2 selection function

Rank is determined independently for each path based on attributes

Each node has a selection function mapping sets of routes to a single “best” route SPP/PVPS GSPP/GPVPS

(10)

Results about GSPP / GPVPS



Ability to model iBGP and complex BGP

features, e.g., MED



Analogous sufficient conditions for

stability in the general case, e.g., the

absence of generalized dispute wheels



Improved space efficiency for methods

(11)

Welfare-Maximizing Routing

AS 1 AS n Mechanism p1 pn vn(.) v1(.) a1 an Private information:

Route valuations Strategies

• Maximize sum of nodes’ valuations = ∑i vi(Ri) .

• A confluent routing tree and payments are computed in parallel for each destination.

• Source nodes are paid for their contribution to the routing tree. • We want a BGP-style algorithm that computes routes and payments.

Routes R1, …, Rn

(12)

SPYCE Results: Welfare Maximization

and Inter-Domain Routing

 

Forbidden Set



(approx. is easy if >1 tree)



(incl. some special cases)

Subjective Cost   Next Hop 

(and hard to approximate)



(and hard to approximate)

General Policy   LCP Good Distributed Algorithm? Good Centralized Algorithm? Routing-Policy Class

(13)

General Approach

 Find a class of policies for which BGP

converges to an optimal tree T (i.e., one that maximizes the sum of the valuations of all source nodes).

 Use VCG payment formula to ensure

truthfulness, i.e., payment to node k is pk = ∑i ≠ k vi(T) – hk(•)

where hk is a function that does not depend on node k’s valuation.

(14)

Gao-Rexford Framework (1)

Neighboring pairs of ASes have one of: - a customer-provider relationship

(One node is purchasing connectivity from the other node.)

- a peering relationship

(Nodes have offered to carry each other’s

transit traffic, often to shortcut a longer route.)

peer

providers

customers peer

(15)

Gao-Rexford Framework (2)

 Global constraint: no customer-provider cycles

 Local preference and scoping constraints, which are

consistent with Internet economics:

 Gao-Rexford conditions => no dispute [GR01, GGR01]

Preference Constraints . . . . . . . . i d R1 R2 k2 k1

• If k1 and k2are both customers, peers, or providers of i, then either ik1R1or ik2R2can be more valued at i.

• If one is a customer, prefer the route through it. If not, prefer the peer route.

Scoping Constraints

d k

i

j

• Export customer routes to all neighbors and export all routes to customers. • Export peer and provider routes to

all customers only.

m . . . . . . . . . . . . peer customer provider

(16)

Realistic Policies for

Incentive-Compatible Routing



Next-hop valuations: The valuation of a

route depends only on its next hop.



Theorem: If ASes obey Gao-Rexford

conditions and next-hop valuations:

- BGP computes the optimal

(welfare-maximizing) routing tree.

- VCG payments can be computed along with routes, with only small increase in routing-table size (like LCP).

(17)

Summary of Sufficient Conditions

No assumptions Hard

(BGP may not converge)

No dispute cycle Non-optimal

(BGP will converge, but

the solution may be arbitrarily far from optimal.)

No dispute cycle

and policy consistency Optimal convergence(but payment computation might be highly space-consuming) No dispute cycle and next-hop valuations (special case of policy consistency) Optimal convergence

and good BGP-style algorithm (Requires O(1) additional space per transit node.)

References

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