Software‐Defined Networking and Network Programmability
Ben Piper · 2020
This chapter differentiates between on-premises and cloud infrastructure deployments. I also explain the working principles of the Cisco SD-WAN and Cisco SD Access solution. When you hear the term software-defined networking (SDN), network automation may not be the first thing that comes to mind. But that's exactly what SDN is. Specifically, SDN is the marriage of network automation with network virtualization and overlays. The advantage of SDN is that it automates the creation of not just overlay networks but underlay networks as well. That means you can make configuration changes faster and with fewer errors. Configuring NAT, IP routing, and VPNs are just a few examples of common configuration tasks that networking professionals are accustomed to doing by hand. SDN hides and automates most of the gnarly configuration steps. To be clear, the same steps still occur behind the scenes, but they're hidden from you. All you have to do is fill in the blanks, so to speak. SDN can also provide automatic remediation and enforce configuration compliance. If something falls out of compliance-for instance, if someone disables OSPF on an interface-the SDN platform can detect it and automatically reenable OSPF. To give another analogy, SDN is like a point-and-click OS GUI, whereas the IOS command line is like an OS's terminal shell. The GUI is easier and sometimes faster. The terminal shell is more complex but more powerful, allowing you to do things that the GUI doesn't. It's not uncommon to hear bombastic talk about how SDN is the future and is going to put “traditional” networking professionals in the unemployment line.