Introduction

VMware NSX provides two mechanisms to achieve routing; the first tier of routing is performed by the Distributed Logical Router (DLR), and the second tier of routing is performed by the Edge services gateway (ESG).

The first tier of routing is known as distributed routing and it's performed by the DLR in the ESXi Hypervisor. Distributed routing is an integral part of any NSX deployment and is usually the first hop for virtual machines that are associated with a logical network; this is because the DLR runs in the ESXi kernel and is highly optimized for "east-west" traffic flows within the data center.

The secondary tier of routing is performed by the ESG. The ESG is a multifaceted device within NSX that provides many different services, but in this chapter, we will only explore its routing capabilities. The ESG comes in a virtual machine form factor and is generally used to provide "north-south" connectivity from virtual networks (logical switches) to the physical network. In some cases it can also be used as the first stop for virtual machines in your network; generally this is not the case when the DLR is used.

When combining the DLR and ESG gateway together, you're able to achieve a routing design that allows virtual machines to communicate with one another (east-west) in the most efficient manner possible and provide connectivity (north-south) to users in the physical network. This combination provides one of the most efficient routing designs for the Data Center using VMware NSX for vSphere.

In the remainder of this chapter, we'll explore the necessary steps to configure distributed routing on the DLR and centralized routing on the ESG. It's necessary to have NSX configured with VXLAN, as described in the first two chapters of this book, before proceeding.

The following diagram provides an overview of the network topology we will be implementing in the recipes following the introduction:

As you can see in the preceding figure, we have chosen to run a dynamic routing protocol between the DLR and ESG; this is not necessary as static routing can also be used. However, the Perimeter ESG may be used to connect to several DLRs, in which case having a dynamic-routing protocol running between all devices makes it easier to exchange routes. In addition, running a dynamic-routing protocol alleviates the task of adding static routing entries to the DLR, ESG, and physical network devices when a new network is added. Lastly, the dynamic-routing protocols supported by NSX are the Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP).