In Step 10, we configured our BGP neighbor and we also configured the forwarding and protocol addresses; understanding what each address is for is important for all the future dynamic routing configurations you may do. This section will explain what each address is used for and how it may impact your routing design.

Let's start by looking at the following figure. We can see a simplified overview of an initial routing topology that depicts the ESG, DLR CVM, and DLR on a Hypervisor:

As you can see, there are three IP addresses assigned to each of the interfaces, and all three IP addresses are in the same subnet. The protocol address is assigned to the DLR control VM and the forwarding address is assigned to the DLR Kernel module LIF. The addresses are used as follows:

• Protocol address: An IP is assigned to the DLR CVM. This address is used to exchange routing updates with the peer router and to send and receive Hello messages.
• Forwarding address: An IP is assigned to the DLR uplink LIF. This is the address where traffic is sent from to the upstream ESG and back from the ESG.

When configuring neighbor relationships with other upstream routers, ensure that you carefully select which two IP addresses to use; the IP addresses must not conflict with any others that may be used in that subnet.