Welcome to the new exciting age of network engineering! When I started working as a network engineer at the turn of the millennium, the role was distinctly different than the network engineering role of today. At the time, network engineers mainly possessed domain-specific knowledge to manage and operate local and wide area networks using the command line interface. While they might occasionally cross over the discipline wall to handle tasks normally associated with systems administration and developers, there was no explicit expectation for a network engineer to write code or understand programming concepts. This is no longer the case today.

Over the years, the DevOps and Software–Defined Networking (SDN) movement, among other factors, have significantly blurred the lines between network engineers, systems engineers, and developers.

The fact that you have picked up this book suggests that you might already be an...

What is the internet? This seemingly easy question might receive different answers depending on your background. The internet means different things to different people; the young, the old, students, teachers, business people, poets, could all give different answers to the same question.

To a network engineer, the internet is a global computer network consisting of a web of inter-networks connecting large and small networks together. In other words, it is a network of networks without a centralized owner. Take your home network as an example. It might consist of a device that integrates the functions of routing, Ethernet switching, and wireless access points connecting your smartphones, tablets, computers, and internet-enabled TVs together for the devices to communicate with each other. This is your local area network (LAN).

When your home network needs to communicate with the outside world, it passes information from your LAN to a larger...

No network book is complete without first going over the OSI model. The model is a conceptional model that componentizes the telecommunication functions into different layers. The model defines seven layers, and each layer sits independently on top of another one with defined structures and characteristics.

For example, in the network layer, IP is located on top of the different types of data link layers, such as Ethernet or frame relay. The OSI reference model is a good way to normalize different and diverse technologies into a set of common languages that people can agree on. This greatly reduces the scope for parties working on individual layers and allows them to look at specific tasks in depth without worrying too much about compatibility:

Figure 4: OSI model

The OSI model was initially worked on in the late 1970s and was later published jointly by the International Organization for Standardization (ISO), what is now known as the Telecommunication...

The client-server reference models demonstrated a standard way for data to communicate between two nodes. Of course, by now, we all know that not all nodes are created equal. Even in the earliest Advanced Research Projects Agency Network (ARPANET) days, there were workstation nodes, and there were server nodes with the purpose of providing content to other nodes. These server nodes typically have higher hardware specifications and are managed more closely by engineers. Since these nodes provide resources and services to others, they are appropriately referred to as servers. Servers typically sit idle, waiting for clients to initiate requests for their resources. This model of distributed resources that are requested by the client request is referred to as the client-server model.

Why is this important? If you think about it for a minute, the importance of networking is greatly highlighted by this client-server model. Without the need to transfer services between...

In the early days of computer networking, protocols were proprietary and closely controlled by the company who designed the connection method. If you were using Novell's IPX/SPX protocol in your hosts, the same hosts would not be able to communicate with Apple's AppleTalk hosts, and vice versa. These proprietary protocol suites generally have analogous layers to the OSI reference model and follow the client-server communication method but are not compatible with each other. The proprietary protocols generally only work in LANs that are closed, without the need to communicate with the outside world. When traffic does need to move beyond the local LAN, typically an internet translation device, such as a router, is used to translate from one protocol to another. For example, in order to connect an AppleTalk-based network to the internet, a router would be used to connect and translate the AppleTalk protocol to an IP-based network. The additional translation...

In a nutshell, this book is about making our network engineering lives easier with Python. But what is Python and why is it the language of choice of many DevOps engineers? In the words of the Python Foundation Executive Summary (https://www.python.org/doc/essays/blurb/):

"Python is an interpreted, object-oriented, high-level programming language with dynamic semantics. Its high-level, built-in data structure, combined with dynamic typing and dynamic binding, makes it very attractive for Rapid Application Development, as well as for use as a scripting or glue language to connect existing components together. Python's simple, easy-to-learn syntax emphasizes readability and therefore reduces the cost of program maintenance."

If you are somewhat new to programming, the object-oriented, dynamic semantics mentioned previously probably do not mean much to you. But I think we can all agree that rapid application development and simple, easy...

In this chapter, we covered the OSI model and reviewed network protocol suites, such as TCP, UDP, and IP. They work as the layers that handle the addressing and communication negotiation between any two hosts. The protocols were designed with extensibility in mind and have largely been unchanged from their original design. Considering the explosive growth of the internet, that is quite an accomplishment.

We also quickly reviewed the Python language, including built-in types, operators, control flows, functions, classes, modules, and packages. Python is a powerful, production-ready language that is also easy to read. This makes the language an ideal choice when it comes to network automation. Network engineers can leverage Python to start with simple scripts and gradually move on to other advanced features.

In Chapter 2, Low-Level Network Device Interactions, we will start to look at using Python to programmatically interact with network equipment.