As the network configurations grow more complex, the requirement for more advanced features such as the source routing features, increases. Source routing is typically used whenever a server is connected to a network (or the Internet) using two network interfaces (see the following image). In this case, it is important to ensure that the connections that are started on one of the interfaces are kept to that interface. If the incoming traffic for a (VPN) connection is made on the first interface but the return traffic is sent back over the second interface, then VPN connections, amongst others, will fail, as we shall see in this recipe.
Source routing is an advanced feature of most of the modern operating systems. In this recipe, we will show how to set up source routing using the Linux iproute2 tools, but the same can be achieved on other operating systems using similar tools.
