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

2. Wonderful problem setting for game theory and mechanism design
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)
Path: 6, 5, 4, 3, 2, 1 4 3 5 2 7 6 1
Web server
Client
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?
“I can reach d via AS 1”
“I can reach d” 1 2 3
data traffic
data traffic d

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 1 3 2 d

7. Policy Conflicts  Convergence Problems
Better choice!
1 2 0
1 0 1
Only choice!
Top choice!
Only choice!
Only choice!
Better choice!
3 1 0
3 0
2 3 0
2 0 3 2
In the meantime, data traffic is going every which way…

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

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 1 2 3 4 d 5 6
Provider-Customer
Peer-Peer 7 8

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

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

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?
1 2 0
1 0 1
3 1 0
3 0
2 3 0
2 0 3 2
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”
Today’s Internet
Tomorrow’s Internet
Hosting “virtual networks” over infrastructure owned by many parties
Competing ASes with different goals must coordinate
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
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