REST API

A REST API (Representational State Transfer Application Programming Interface) is a set of rules that allows systems to communicate using the HTTP protocol, the same protocol your browser uses to access websites.

Imagine managing hundreds of network devices without typing a single CLI command. That’s the power of REST APIs. They allow software to communicate directly with your network devices to automate repetitive configuration and monitoring tasks.

Why REST APIs Matter in Networking

In traditional networking, engineers connect manually to each device to configure them one by one. With REST APIs, a single request can apply changes, collect data, or perform actions across multiple devices simultaneously.

Figure 1 - Manual CLI vs REST API automation across multiple devices.

This fundamental difference is what enables network automation, using software or controllers to push configurations, gather information, and maintain consistency efficiently across the entire network.

In network automation, REST APIs are often used to exchange information between automation tools and network devices.

This communication typically involves three components: REST API Client (like your automation script), a REST API Server, and a Network Device.

Each of them plays a distinct role in sending, processing, and responding to requests.

Understanding the Client–Server Model

The REST API follows a client–server model where each side has a clear responsibility.

• The client sends an HTTP request to perform an action, such as retrieving, creating, updating, or deleting data.
  

• The server interprets the request, interacts with the interested device, and then returns a response to the client.

Figure 2 – REST API Client–Server Communication Model

As shown in Figure 3, the REST API client sends an HTTP GET request to the API server, which forwards it to the network device.

Once the device responds, the server sends the data back to the client in a structured format such as JSON.

In simple terms, the client sends a request, the API server processes it, and the device returns a response with the required data. This model is at the heart of network automation, allowing consistent and scalable communication between systems.

REST APIs use HTTP methods to describe the type of action you want to perform.
These actions follow the CRUD model, which stands for:

• Create – add new data

• Read – retrieve existing data

• Update – modify existing data

• Delete – remove data

Each CRUD action corresponds to a specific HTTP method used in network automation.

Table 1 - CRUD Methods Overview

Each method works like a verb in a sentence.
It defines what kind of action you’re asking the API to perform.

For example:

• A GET request retrieves information, such as interface status or device inventory.

• A POST request creates a new resource, like adding VLAN 20 to a switch.

• A PUT request updates an existing configuration, for instance changing all interface settings.

• A PATCH request modifies a specific field, such as updating only an interface description.

• A DELETE request removes an existing resource, like deleting VLAN 10 from the device.

These simple verbs form the foundation of REST API communication.
Once you understand them, you can interpret any REST request and know exactly what it is designed to do.

Once you’ve defined what action you want to perform, you also need to specify where you want to act.
That’s the purpose of the URI (Uniform Resource Identifier).