A Scalability Study of Enterprise Network Architectures

The largest enterprise networks already contain hundreds of thousands of hosts. Enterprise networks are composed of Ethernet subnets interconnected by IP routers. These routers require expensive configuration and maintenance. If the Ethernet subnets are made more scalable, the high cost of the IP routers can be eliminated. Unfortunately, it has been widely acknowledged that Ethernet does not scale well because it relies on broadcast, which wastes bandwidth, and a cycle-free topology, which poorly distributes load and forwarding state. There are many recent proposals to replace Ethernet, each with its own set of architectural mechanisms. These mechanisms include eliminating broadcasts, using source routing, and restricting routing paths. Although there are many different proposed designs, there is little data available that allows for comparisons between designs. This study performs simulations to evaluate all of the factors that affect the scalability of Ethernet together, which has not been done in any of the proposals. The simulations demonstrate that, in a realistic environment, source routing reduces the maximum state requirements of the network by over an order of magnitude. About the same level of traffic engineering achieved by load-balancing all the flows at the TCP/UDP flow granularity is possible by routing only the heavy flows at the TCP/UDP granularity. Additionally, requiring routing restrictions, such as deadlock-freedom or minimum-hop routing, can significantly reduce the network's ability to perform traffic engineering across the links.