Can Economic Incentives Make the ‘Net Work?

Jennifer RexfordPrinceton University

http://www.cs.princeton.edu/~jrex

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What is an Internet?

• A “network of networks”–Networks run by different institutions

• Autonomous System (AS)–Collection of routers run by a single institution

• ASes have their own local goals–E.g., different views of which paths are good

• Interdomain routing reconciles those views–Computes end-to-end paths through the Internet

Wonderful problem setting for game theory and mechanism design

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Three Parts to This Talk

• Today’s interdomain routing–Protocol allows global oscillation to occur–Yet, rational behavior ensures global stability

• Improving today’s interdomain routing–Today’s routing system is not flexible enough–Allow greater flexibility while ensuring stability

• Rethinking the Internet routing architecture–Refactoring the business relationships entirely–Raising a host of new open questions…

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Autonomous Systems (ASes)

1

2

3

4

5

67

ClientWeb server

Path: 6, 5, 4, 3, 2, 1

Around 35,000 ASes today…

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Border Gateway Protocol (BGP)

• ASes exchange reachability information–Destination: block of IP addresses–AS path: sequence of ASes along the path

• Policies “programmed” by network operators–Path selection: which path to use?–Path export: which neighbors to tell?

1 2 3

d

“I can reach d”“I can reach d via AS 1”

data traffic data traffic

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Stable Paths Problem (SPP) Model

• Model of routing policy– Each AS has a ranking of the permissible paths

• Model of path selection– Pick the highest-ranked path consistent with neighbors

• Flexibility is not free– Global system may not converge to a stable assignment– Depending on the way the ASes rank their paths

1 2 d1 d

2 3 d2 d

3 1 d3 d

1

3

2

d

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Policy Conflicts Convergence Problems

0

1

23

1 2 01 0

2 3 02 0

3 1 03 0

In the meantime, data traffic is going every which way…

Only choice!

Top choice!

Only choice!

Better choice!

Only choice!

Better choice!

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Ways to Achieve Global Stability

• Detect conflicting rankings of paths?– Computationally intractable (NP-hard)– Requires global coordination

• Restrict the policy configuration languages?– In what way? How to require this globally?– What if the world should change, and the protocol can’t?

• Rely on economic incentives?– Policies typically driven by business relationships– E.g., customer-provider and peer-peer relationships– Sufficient conditions to guarantee unique, stable solution

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Bilateral Business Relationships

• Provider-Customer– Customer pays provider for access to the Internet

• Peer-Peer– Peers carry traffic between their respective customers

2 3

1

d

4

5 6

7 8

Provider-Customer

Peer-Peer

Valid paths: “1 2 d” and “7 d”Invalid path: “5 8 d”Valid paths: “6 4 3 d” and “8 5 d”

Invalid paths: “6 5 d” and “1 4 3 d”

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Act Locally, Prove Globally

• Global topology– Provider-customer relationship graph is acyclic– Peer-peer relationships between any pairs of ASes

• Route export– Do not export routes learned from a peer or provider– … to another peer or provider

• Route selection– Prefer routes through customers– … over routes through peers and providers

• Guaranteed to converge to unique, stable solution

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Rough Sketch of the Proof

• Two phases– Walking up the customer-provider hierarchy– Walking down the provider-customer hierarchy

2 3

1

d

4

5 6

7 8

Provider-Customer

Peer-Peer

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Trade-offs Between Assumptions

• Three kinds of assumptions–Route export, route selection, global topology–Relax one, must tighten the other two

• Are these assumptions reasonable?–Could business practices change over time?

• Two unappealing features–An AS picks a single best route–An AS must prefer routes through customers

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A Case For Customized Route Selection

• ISPs usually have multiple paths to the destination

• Different paths have different properties

• Different neighbors may prefer different routes

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Bank

VoIPprovider

School

Most secureShortest latency

Lowest cost

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Neighbor-Specific Route Selection

• A node has a ranking function per neighbor

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i

j is node i’s ranking function for neighbor node j.

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Stability Conditions for NS-BGP

• Surprisingly, NS-BGP improves stability!–Neighbor-specific selection is more flexible–Yet, requires less restrictive stability conditions

• “Prefer customer” assumption is not needed–Choose any “permissible” route per neighbor

• That is, need just two assumptions–No cycle of provider-customer relationships–An AS does not export routes learned from one

peer or provider to other peers or providers

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Why Do Weaker Conditions Work?

• An AS always tells its neighbor a route– If it has any route that is permissible for that neighbor

0

1

23

1 2 01 0

2 3 02 0

3 1 03 0

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Customized Route Selection

• Customized route selection as a service– Select a different best route for different neighbors

• Different menu options– Cheapest route (e.g., “prefer customer”)– Best performing routes– Routes that avoid undesirable ASes (e.g., censorship)

• Nice practical features of NS-BGP– An individual AS can deploy NS-BGP alone– … and immediately gain economic value– Without compromising global stability!

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Looking Forward: “Cloud Networking”

– InToday’s Internet

Competing ASes with different goals must coordinate

Tomorrow’s Internet

Hosting “virtual networks” over infrastructure owned by many parties

• Infrastructure providers: Own routers, links, data centers

• Service providers: Offer end-to-end services to users

Economics play out vertically on a coarser timescale.

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Advantages of Virtual Networks

• Simplifies deployment of new technologies–Easier to deploy in a single (virtual) network–Multicast, quality-of-service, security, IPv6, …

• Enables the use of customized protocols–Secure addressing & routing for online banking–Anonymity for Web browsing–Low delay for VoIP and gaming

• Greater accountability–Direct relationship with infrastructure providers–Account for performance/reliability of virtual links

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Conclusions

• Internet is a network of networks– Tens of thousands of Autonomous Systems (ASes)

• Network protocols are very flexible– To enable autonomy and extensibility

• Global properties are not necessary ensured– Stability, efficiency, reliability, security, managability, …

• Economic incentives sometimes save the day– E.g., rational local choices ensure global stability

• Are we willing to rely on economic motivations?– Do we have any choice?

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References Related to This Talk

• “The stable paths problem and interdomain routing”– Tim Griffin, Bruce Shepherd, and Gordon Wilfong– http://portal.acm.org/citation.cfm?id=508332

• “Stable Internet routing without global coordination”– Lixin Gao and Jennifer Rexford– http://www.cs.princeton.edu/~jrex/papers/sigmetrics00.long.pdf

• "Neighbor-Specific BGP: More flexible routing policies while improving global stability“– Yi Wang, Michael Schapira, and Jennifer Rexford– http://www.cs.princeton.edu/~jrex/papers/nsbgp_sigmetrics09.pdf

• "How to lease the Internet in your spare time" – Nick Feamster, Lixin Gao, and Jennifer Rexford– http://www.cs.princeton.edu/~jrex/papers/cabo-short.pdf

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Other Related Research Papers• Inherently Safe Backup Routing with BGP

– http://www.cs.princeton.edu/~jrex/papers/infocom01.pdf

• Design Principles of Policy Languages for Path Vector Protocols– http://conferences.sigcomm.org/sigcomm/2003/papers/p61-griffin.pd

f

• Implications of Autonomy for the Expressiveness of Policy Routing– http://conferences.sigcomm.org/sigcomm/2005/paper-FeaBal.pdf

• Metarouting– http://conferences.sigcomm.org/sigcomm/2005/paper-GriSob.pdf

• An Algebraic Theory of Interdomain Routing– http://portal.acm.org/citation.cfm?id=1103561

• Searching for Stability In Interdomain Routing– http://www.cs.yale.edu/homes/schapira/PID808559.pdf

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Related Papers With Game Theory• Interdomain Routing and Games

– http://www.cs.huji.ac.il/~mikesch/routing_games-full.pdf

• Rationality and Traffic Attraction: Incentives for Honest Path Announcements in BGP

– http://ccr.sigcomm.org/online/?q=node/395

• Incentive-Compatible Interdomain Routing– http://cs-www.cs.yale.edu/homes/jf/FRS.pdf

• Mechanism Design for Policy Routing– http://cs-www.cs.yale.edu/homes/jf/FSS.pdf

• The Complexity of Game Dynamics: BGP Oscillations, Sink Equlibria, and Beyond

– http://www.cs.berkeley.edu/~alexf/papers/fp08.pdf

• Specification Faithfulness in Networks with Rational Nodes – http://www.eecs.harvard.edu/econcs/pubs/podc04.pdf

• Distributed Algorithmic Mechanism Design – http://cs-www.cs.yale.edu/homes/jf/AGTchapter14.pdf

• Partially Optimal Routing– http://www.stanford.edu/~rjohari/pubs/por.pdf

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Background on Interdomain Economics

• http://drpeering.net/a/Home.html

• http://www.fcc.gov/Bureaus/OPP/working_papers/oppwp32.pdf

• http://www.potaroo.net/papers/1999-6-peer/peering.pdf

• http://www.cisco.com/en/US/about/ac123/ac147/ac174/ac201/about_cisco_ipj_archive_article09186a00800c83a5.html

• http://www.cisco.com/en/US/about/ac123/ac147/ac174/ac200/about_cisco_ipj_archive_article09186a00800c8900.html

• http://www.vjolt.net/vol3/issue/vol3_art8.html