The evolution of current data centers is driven by several major forces in terms of end-user and service requirements. Tenants, using infrastructures as a service (IaaS), require large Internet protocol (IP) address spaces operated over multiple physical networks, mobility of virtual machines, and operation in hybrid environments consisting of physical and virtual infrastructures. One of the core enablers for meeting these requirements is to provide scalable overlay networks capable of virtualizing layer 2 over existing layer 3 protocols. Several such approaches exist: virtual extensible LAN (VXLAN), NGVRE, FabricPath, and TRILL are the major players in the field, where a conceptual design is common to all these protocols.

This design relies on encapsulating layer 2 traffic in layer 3 traffic, but subtle differences among them relate to how link-state routing protocols like intermediate system to intermediate system (IS-IS) and open shortest path first (OSPF) can be leveraged to transparently build such overlays. The fundamental question that has to be solved by these protocols is essentially very simple. Once layer 2 traffic is encapsulated in a layer 3 packet, the routing needs to map media access control (MAC) addresses to tunnel endpoints identified by layer 3 addresses. This process is the major discriminator among VXLAN, NGVRE, and Trill, and the authors go into great detail in describing it.

Chapter 1 motivates the need for overlay networks. Chapter 2 provides a high-level overview on the different overlay technologies, followed by individual chapters on FabricPath, TRILL, and VXLAN, respectively. What makes this book truly exceptional is the right mix of graphical illustrations, concrete device instantiations, and hands-on concrete command-line interface (CLI) examples. The logical flow of this book is a blueprint on how to write a technical book. Besides just a simple enumeration of major overlay technologies, the book dedicates significant coverage to the migration of existing infrastructures toward TRILL. Both bottom-up and top-down alternatives are discussed. Combining TRILL with VXLAN in one unified overlay is not straightforward, and the authors address this specific issue in the last chapter of the book.

This book fills an existing niche in the computer networking literature. Several Internet Engineering Task Force (IETF) standards and scattered pieces of information were, until now, the required entry point to the design of network overlays. The Cisco team manages to write a comprehensive introduction to this timely topic, with an updated, precise, and well-thought-out book in the area. This book is a welcome recommendation for a large audience: network designers, network engineers, and cloud operators can learn and benefit from it.

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