Experiences in building a multihoming load balancing system

The growing popularity of consumer broadband connection technology, in particular cable TV and ADSL, has started a quiet revolution that will reshape the Internet connectivity solutions for commercial enterprises. One emerging theme is the replacement of dedicated lines based on frame relay or ISDN technologies with multiple inexpensive ADSL/cable TV links each of which potentially is subscribed from a different ISP. The key enabling technology for this revolution is multihoming load balancing, which spreads an enterprise´s Internet traffic among multiple access links to increase the aggregate throughput, and diverts traffic away from non-functional links when they fail. Although there exist several commercial multihoming load balancing products in the marketplace, very little is published about the design tradeoffs and their performance implications. We describe the design space of multihoming load balancing systems, discuss the tradeoffs involved in load balancing and fail-over implementation strategies, and present quantitative performance measurements collected on a commercial multihoming load balancing system.