1. Improving BGP Convergence Through Consistency Assertions Dan Pei, Lan Wang, Lixia Zhang UCLA Xiaoliang Zhao, Daniel Massey, Allison Mankin, USC/ISI S. Felix Wu UC-Davis

2. 2 Internet: composed of thousands of Autonomous Systems(ASes). BGP Background BGP (Border Gateway Protocol): the de facto inter-AS routing protocol AS A R1 R2 R3 AS B AS C R4 R5 AS E R6 BGP Routers

3. 3 How BGP works Uses path vector protocol similar to distance vector protocol. what if no path available? Consider an AS as a node Route via A = Route via C = B’s route to D: route includes entire path(sequence of nodes) D A B C E D:

4. 4 BGP’s Slow Convergence B’s route to D Route via A= Route via C= D A B C E Obsolete backup path is used, and convergence is delayed withdraw Our approach: B can immediately recognize that path is obsolete since it also used A. Route via A= Route via C= B quickly realizes there is no path to D  convergence. withdrawal sent if no path available A B C E

5. 5 Policy Withdrawal But A could stop advertising to B due to a policy change, path is still valid! ABCE policy withdraw D Attach a Failure Withdrawal Community Attribute Only apply the approach to failure withdrawal B’s route to D Route via A= Route via C= Route via A= A B C E

6. 6 BGP Traffic Engineering BGP Traffic Engineering: R4 chooses path R5 chooses path We assumed an AS could be modeled as a node with a single best path to the destination But a single AS may advertise more than one path. Divide one AS into Logical ASes such that All routers within a logical AS have the same best path  each logical AS can be modeled as a node.

7. 7 Simulation Setting Implemented our approach in SSFNet simulator from http://www.ssfnet.org. http://www.ssfnet.org Topology derived from BGP tables at Oregon Router Views Server Measure the convergence time and number of updates, compare the results of original BGP with enhanced BGP

8. 8 Performance Comparison: Number of Updates Number of ASes in Network Number of Updates Original BGP Enhanced BGP Substantial reduction is achieved. E.g. 3766 to 1419 in the 60-AS topology MinRouteAdver timer: within 30 seconds, only one advertisement is allowed. It “packs” consecutive changes into one update.

9. 9 Performance Comparison: Convergence time Number of ASes in Network Convergence Time(seconds) Original BGP Enhanced BGP Enhanced BGP reduces the convergence time substantially. E.g. 337.0 seconds to 19.5 seconds in the 60- AS topology Elimination of one advbertisement can cut convergence time by 30 seconds

10. 10 Summary Instead of blindly accepting all BGP updates, check route consistency using the information that a router has learned from previous updates and from other neighbors. BGP convergence time is substantially reduced by checking AS Path Information. Route Change, formalization, and implementation in paper The “checking before accepting” idea can also improve BGP’s fault tolerance, see our other papers at http://fniisc.nge.isi.edu http://fniisc.nge.isi.edu

11. 11 Thank you! Questions?