Can Economic Incentives Make the ‘Net Work? Jennifer Rexford Princeton University

2 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

3 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…

4 Autonomous Systems (ASes) Client Web server Path: 6, 5, 4, 3, 2, 1 Around 35,000 ASes today…

5 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 23 d “I can reach d” “I can reach d via AS 1” data traffic

6 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 d 1 d 2 3 d 2 d 3 1 d 3 d d

7 Policy Conflicts  Convergence Problems In the meantime, data traffic is going every which way… Only choice! Top choice! Only choice! Better choice! Only choice! Better choice!

8 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

9 Bilateral Business Relationships Provider-Customer –Customer pays provider for access to the Internet Peer-Peer –Peers carry traffic between their respective customers d 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”

10 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

11 Rough Sketch of the Proof Two phases –Walking up the customer-provider hierarchy –Walking down the provider-customer hierarchy d Provider-Customer Peer-Peer

12 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

13 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 13 Bank VoIP provider School Most secure Shortest latency Lowest cost

14 Neighbor-Specific Route Selection A node has a ranking function per neighbor 14 is node i’s ranking function for neighbor node j.

15 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

16 Why Do Weaker Conditions Work? An AS always tells its neighbor a route –If it has any route that is permissible for that neighbor

17 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!

18 Looking Forward: “Cloud Networking” –In Today’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.

19 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

20 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?

21 References Related to This Talk “The stable paths problem and interdomain routing” –Tim Griffin, Bruce Shepherd, and Gordon Wilfong – “Stable Internet routing without global coordination” –Lixin Gao and Jennifer Rexford – "Neighbor-Specific BGP: More flexible routing policies while improving global stability“ –Yi Wang, Michael Schapira, and Jennifer Rexford – "How to lease the Internet in your spare time" –Nick Feamster, Lixin Gao, and Jennifer Rexford –

22 Other Related Research Papers Inherently Safe Backup Routing with BGP – Design Principles of Policy Languages for Path Vector Protocols – griffin.pdfhttp://conferences.sigcomm.org/sigcomm/2003/papers/p61- griffin.pdf Implications of Autonomy for the Expressiveness of Policy Routing – Metarouting – An Algebraic Theory of Interdomain Routing – Searching for Stability In Interdomain Routing –

23 Related Papers With Game Theory Interdomain Routing and Games – Rationality and Traffic Attraction: Incentives for Honest Path Announcements in BGP – Incentive-Compatible Interdomain Routing – Mechanism Design for Policy Routing – The Complexity of Game Dynamics: BGP Oscillations, Sink Equlibria, and Beyond – Specification Faithfulness in Networks with Rational Nodes – Distributed Algorithmic Mechanism Design – Partially Optimal Routing –

24 Background on Interdomain Economics /about_cisco_ipj_archive_article09186a00800c83a5.htmlhttp:// 01/about_cisco_ipj_archive_article09186a00800c83a5.html 00/about_cisco_ipj_archive_article09186a00800c8900.htmlhttp:// 00/about_cisco_ipj_archive_article09186a00800c8900.html