No man is an island, entire of itself; every man is a piece of the continent
Like men, data centers are not islands unto themselves. This chapter is about how they connect to the rest of world. The chapter should help you answer questions such as:
In what ways can a Clos topology can be connected to an external network?
What are best practices for deploying a routing protocol at the edge?
How does an enterprise handle connectivity in a hybrid cloud?
Connectivity to the external world is a north-south traffic pattern, as described in Directionality in Network Diagrams. A fundamental driver for the selection of the Clos topology was its ability to handle east-west traffic patterns well. Let us now examine how to connect a network built using Clos topology to the external world. The answers to the following questions govern several factors that affect the connectivity of a data center to the external world:
Why is the external connectivity required?
What are the bandwidth demands of the connection to the external world?
What upstream device will the data center network be connected to?
What services are necessary for any traffic crossing the internal-to-external world?
The answer to the first two questions lead us to a choice between models for connecting to the external world. The next two questions guide the remainder of the edge connectivity discussion. The first question also leads us ...