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Scalable network infrastructure in Layer 3 with BGP

Growth Spurt

Article from ADMIN 40/2017

By Martin Loschwitz

Large environments such as clouds pose demands on the network, some of which cannot be met with Layer 2 solutions. The Border Gateway Protocol jumps into the breach in Layer 3 and ensures seamlessly scalable networks.

Large-scale virtualization environments have ousted typical small setups. Whereas a company previously purchased a few physical servers to deploy an application, today, the entire workload of a new setup ends up on virtual machines running on a cloud service provider's platform.

A physical layout often is based on a tree structure (Figure 1), with the admin connecting all the servers to one or two central switches and adding more switches if the number of ports on a switch is not sufficient. Together, the switches and network adapters form a large physical segment in OSI Layer 2.

Figure 1: Classic network architectures that follow a tree structure are not suitable for scale-out platforms.

In this article, I describe how you can build an almost arbitrarily scalable network for your environments with Layer 3 tools. As long as two hosts have any kind of physical communication path, communication on Layer 3 works, even if the hosts in question reside in different Layer 2 segments. The Border Gateway Protocol (BGP) makes this possible by providing a way to let each server know how to reach other servers; "IP fabric" describes data center interconnectivity via IP connections.

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