What is an API and How Does it Work?

If you've spent any time reading about network automation, you've almost certainly come across the term API. It gets thrown around constantly, but for someone just getting started, it can feel like an abstract concept. Let's break it down in plain language and connect it directly to the world of networking.

What is an API?

API stands for Application Programming Interface. At its core, an API is a defined way for two pieces of software to communicate with each other. Think of it as a contract between applications: one side says "here's what you can ask me, and here's exactly how to ask it," and the other side sends requests and receives responses in that agreed-upon format.

A common real-world analogy is a restaurant menu. You don't walk into the kitchen and cook your own food. Instead, you look at the menu (the interface), place an order (the request), and the kitchen (the backend system) prepares what you asked for and sends it back to your table (the response). You never need to know how the kitchen works internally.

How Does an API Actually Work?

In networking and automation contexts, you'll most commonly work with REST APIs (Representational State Transfer). These APIs use standard HTTP methods to perform actions on a system. The four most common methods are:

• GET: Retrieve information from a device or system
• POST: Send new data or create a new resource
• PUT: Update an existing resource
• DELETE: Remove a resource

Every API call is made to a specific endpoint, which is just a URL that points to a particular resource on the system. For example, if you were querying a Cisco DNA Center controller for a list of devices, you might send a GET request to an endpoint like:

GET https://sandboxdnac.cisco.com/dna/intent/api/v1/network-device

The system receives that request, processes it, and sends back a structured response, usually in JSON (JavaScript Object Notation) format. JSON is easy for both humans and programs to read, which makes it the dominant format for modern REST APIs.

A simplified JSON response from a network device query might look like this:

{
  "response": [
    {
      "hostname": "switch1.lab.local",
      "managementIpAddress": "10.10.1.1",
      "platformId": "C9300-48P",
      "softwareVersion": "17.3.3"
    }
  ]
}

Why Do APIs Matter in Networking?

Traditionally, network engineers configured devices manually through a CLI, one command at a time. APIs change that model completely. Instead of SSH-ing into each device individually, you can write a script or use a tool that calls an API once and retrieves or configures information across your entire network programmatically.

Here's what that means practically:

• Speed: A Python script using an API can query 200 devices in seconds
• Consistency: Every request follows the same format, reducing human error
• Integration: APIs allow different platforms to talk to each other; your monitoring tool can pull data from your controller automatically
• Automation: Provisioning, compliance checks, and troubleshooting workflows can all be triggered via API calls

Cisco platforms like DNA Center, Meraki, and the NSO orchestrator all expose REST APIs. Understanding how to interact with them is a core skill for the CCNA DevNet exam and for modern network engineering in general.

A Quick Summary of API Basics

Before moving on, here are the key concepts to remember:

• An API is a defined interface that lets software communicate with other software
• REST APIs use HTTP methods: GET, POST, PUT, and DELETE
• Requests are sent to specific endpoints (URLs), and responses are typically returned in JSON format
• In networking, APIs replace or supplement manual CLI work, enabling automation at scale

What's Next?

Now that you understand what an API is and how it functions conceptually, the next step is learning how to actually make API calls. In the next post, we'll look at using Postman to send your first real API requests to a Cisco sandbox environment, no Python required. It's the fastest way to get hands-on with APIs and build confidence before writing any code.

If you want to go deeper on this topic alongside your exam prep, the Cisco Press CCNA DevNet Associate DEVASC 200-901 Official Cert Guide covers APIs thoroughly and maps directly to the exam blueprint.