SmartBridge: A Scalable Bridge Architecture
Darrell Anderson, Duke University
I spent my summer working with Tom Rodeheffer and Chandu Thekkath
on SmartBridge, a scalable bridge architecture supporting automatic
reconfiguration and shortest path routing in ethernet. We built a
software prototype inside the FreeBSD kernel, SmartBridging between
ethernet adapters. We observed a dozen bridge reconfiguration times
around 10 ms and found that our solution performed as well as a
Prominet Cajun hardware bridge
in terms of latency and throughput for a single session on 100 Mb/s
ethernet.
Introduction
As the number of hosts in a network exceeds what an ethernet segment
can handle, bridges are employed to partition the network into
multiple segments, routing traffic between them. Two common solutions
for routing in a network are IP routing and bridge routing. The
former approach connects networks at the IP layer and is known to
scale well. However, individual hosts and IP routers need to be
configured by hand. Bridge routing, in contrast, works at the link
layer, is transparent to the host, and is automatic to set up.
Unfortunately, bridge routing does not scale well because traffic is
carried along a spanning tree where a single bridge can become a
bottleneck.
This project introduces a new architecture called SmartBridge that
combines the good features of IP routing and bridge routing.
SmartBridges offer an advantage over ordinary bridges in that they
perform shortest path routing, introducing fewer bottlenecks in large
networks. They offer an advantage over IP routers in that they are
automatic to set up (no host configuration), easy to administer, and
incrementally scalable with little or no operator intervention.
What's Interesting?
Here were the main action items of the project:
- Learning global network topology (à la Autonet).
- Finding deterministic shortest-path routes in linear time.
- Locating hosts on segments.
- Propagating host location without introducing routing loops.
- Recognizing host movement.
- Setting up peaceful coexistence with standard bridges (which
included redundant links).
Acknowledgments
I would like to thank Tom Rodeheffer, my host, for introducing me
to the finer points of bridge routing. Chandu Thekkath was my co-host and
had many helpful suggestions. Mitch Lichtenburg assisted with the
initial setup and final experiments with contemporary hardware.
Leslie Lamport and Ed Lee helped keep me in shape--and thanks also to
Mike Burrows for advice and entertainment.
About the Author
I began my Ph.D. program at Duke University in the fall of 1996,
working with Jeff Chase on gigabit networking and storage interaction.
About the Author's Pet Iguana
I don't have a pet iguana. I just wanted to say I had a terrific
summer and I figure this way you're more likely to read it. During my
stay, I learned a great deal about distributed algorithms,
professional life outside academia, and specialty coffees. Thanks!