Let's start with a simple question: What is routing? Routing, in computer science or in telecommunication, means defining paths (or rather more precisely, defining the entire path, including all way-points) for message streams during message transmission in a network.

This is a very general explanation and therefore we should now look at the topic of routing in the area of Azure networking. For Azure networking, packet-switched routing is generally used. This is the same routing method which is also the basis of the internet.

What is packet-switched routing? In packet-switched routing, it is ensured that logically addressed data packets emerge from the originating network and are forwarded to their destination network. The data packets can pass many different intermediate networks on their way to their destination.

To know where packets are to be sent, the structure of the network must be known. In small networks, the information required for routing is easily configured manually. For large networks with very complex topologies, which may change often, capture is often dynamic.

Since routing can only very slowly determine the best paths relative to the number of packets to be moved, the best possible paths are stored in one or more routing tables. Also, Azure networking uses a standard routing table for its work.

Why do I tell you this? Ok so far, it was a general description of how it works. But there are exceptions (or specialties) which I will introduce to you now.