An Introduction to Networking Terminology, Interfaces, and Protocols

An understanding of networking is important for anyone managing a server. Not only is it essential for getting your services online and running smoothly, it also gives you the insight to diagnose problems.

This article will provide an overview of some common networking concepts. We will discuss terminology, common protocols, and the responsibilities and characteristics of the different layers of networking.

This guide is operating system agnostic, but should be very helpful when implementing features and services that utilize networking on your server.

First, we will define some common terms that you will see throughout this guide, and in other guides and documentation regarding networking.

These terms will be expanded upon in the appropriate sections that follow:

• Connection: In networking, a connection refers to pieces of related information that are transferred through a network. Generally speaking, a connection is established before data transfer (by following the procedures laid out in a protocol) and may be deconstructed at the end of the data transfer.

• Packet: A packet is the smallest unit that is intentionally transferred over a network. When communicating over a network, packets are the envelopes that carry your data (in pieces) from one end point to the other.

Packets have a header portion that contains information about the packet including the source and destination, timestamps, network hops, etc. The main portion of a packet contains the actual data being transferred. It is sometimes called the body or the payload.

• Network Interface: A network interface can refer to any kind of software interface to networking hardware. For instance, if you have two network cards in your computer, you can control and configure each network interface associated with them individually.

A network interface may be associated with a physical device, or it may be a representation of a virtual interface. The “loopback” device, which is a virtual interface available in most Linux environments to connect back to the same machine, is an example of this.

• LAN: LAN stands for “local area network”. It refers to a network or a portion of a network that is not publicly accessible to the greater internet. A home or office network is an example of a LAN.

• WAN: WAN stands for “wide area network”. It means a network that is much more extensive than a LAN. While WAN is the relevant term to use to describe large, dispersed networks in general, it is usually meant to mean the internet, as a whole.

If an interface is said to be connected to the WAN, it is generally assumed that it is reachable through the internet.

• Protocol: A protocol is a set of rules and standards that define a language that devices can use to communicate. There are a great number of protocols in use extensively in networking, and they are often implemented in different layers.

Some low level protocols are TCP, UDP, IP, and ICMP. Some familiar examples of application layer protocols, built on these lower protocols, are HTTP (for accessing web content), SSH, and TLS/SSL.

• Port: A port is an address on a single machine that can be tied to a specific piece of software. It is not a physical interface or location, but it allows your server to be able to communicate using more than one application.

• Firewall: A firewall is a program that decides whether traffic coming or going from a server should be allowed. A firewall usually works by creating rules for which type of traffic is acceptable on which ports. Generally, firewalls block ports that are not used by a specific application on a server.

• NAT: NAT stands for network address translation. It is a way to repackage and send incoming requests to a routing server to the relevant devices or servers on a LAN. This is usually implemented in physical LANs as a way to route requests through one IP address to the necessary backend servers.

• VPN: VPN stands for virtual private network. It is a means of connecting separate LANs through the internet, while maintaining privacy. This is used to connect remote systems as if they were on a local network, often for security reasons.

There are many other terms that you will come across, and this list is not exhaustive. We will explain other terms as we need them. At this point, you should understand some high-level concepts that will enable us to better discuss the topics to come.

While networking is often discussed in terms of topology in a horizontal way, between hosts, its implementation is layered in a vertical fashion within any given computer or network.

What this means is that there are multiple technologies and protocols that are built on top of each other in order for communication to function. Each successive, higher layer abstracts the raw data a little bit more.

It also allows you to leverage lower layers in new ways without having to invest the time and energy to develop the protocols and applications that handle those types of traffic.

The language that we use to talk about each of the layering schemes varies significantly depending on which model you use. Regardless of the model used to discuss the layers, the path of data is the same.

As data is sent out of one machine, it begins at the top of the stack and filters downwards. At the lowest level, actual transmission to another machine takes place. At this point, the data travels back up through the layers of the other computer.

Each layer has the ability to add its own “wrapper” around the data that it receives from the adjacent layer, which will help the layers that come after decide what to do with the data when it is handed off.

Interfaces are networking communication points for your computer. Each interface is associated with a physical or virtual networking device.

Typically, your server will have one configurable network interface for each Ethernet or wireless internet card you have.

In addition, it will define a virtual network interface called the “loopback” or localhost interface. This is used as an interface to connect applications and processes on a single computer to other applications and processes. You can see this referenced as the “lo” interface in many tools.

Many times, administrators configure one interface to service traffic to the internet and another interface for a LAN or private network.

In datacenters with private networking enabled (including DigitalOcean Droplets), your VPS will have two networking interfaces. The “eth0” interface will be configured to handle traffic from the internet, while the “eth1” interface will operate to communicate with a private network.

Networking works by piggybacking a number of different protocols on top of each other. In this way, one piece of data can be transmitted using multiple protocols encapsulated within one another.

We will start with protocols implemented on the lower networking layers and work our way up to protocols with higher abstraction.

At this point, you should be familiar with some networking terminology and be able to understand how different components are able to communicate with each other. This should assist you in understanding other articles and the documentation of your system.

Next, for a high-level, read world example, you may want to read How To Make HTTP Requests in Go.