JSON

For the CCNA exam, you need to be able to understand and interpret JSON (JavaScript Object Notation).
To begin this lesson, we will answer two questions:

• Why do we need JSON?

• What problem does JSON solve in networking?

Let’s start with a simple example.

Why we need JSON

Imagine you are using a network monitoring application.
This application needs to regularly check the status of interfaces on multiple routers to make sure the network is operating correctly.

Figure 1 - Network monitoring application requesting interface status information

Modern network devices provide APIs that allow applications to request this information.

At first glance, this seems simple:

• the monitoring application sends a GET request

• the router replies with the requested information

The Problem Without a Standard Format

Figure 2 illustrates this process.

1. The monitoring application sends a GET request to the router.

2. The router accesses its internal variables, such as interface status and IP address.

3. The router sends the information back without a standardized format, making the response not machine-readable.

Figure 2 – Interface information exchanged without a standardized format

However, this is where the problem appears.
The router cannot simply send its raw internal variables back to the application in a usable form.

Internal device variables:

• are designed for the router’s operating system

• are not readable by external applications

As a result, the monitoring application cannot interpret the data directly.

JSON as the Standard Data Format

We need a standard and structured format to exchange system information.

This format must be:

• readable by machines

• vendor-independent

• easy to parse

JSON is used to represent internal device variables in a standard format that can be exchanged over the network.
This is called a data format.

Let’s return to our example.

1. The monitoring application sends an API request to the router.

2. The router checks its internal variables to retrieve the requested information.

3. These internal variables are then converted into JSON format by the API.

4. The information is sent to the monitoring application encoded in JSON.

Figure 3 – Interface variables exchanged using JSON format

When the monitoring application receives the JSON message:

• it reads the structured data

• it extracts the values

• it converts them into its own internal representation

In this way, different devices and applications are able to exchange data using the same standard format.

Now that we understand why JSON is used in networking, we need to learn what a JSON message represents.

Figure 4 - JSON data exchange

To do this, we will start with something you already know well: the Cisco CLI.

Checking Interface Information with the CLI

When we check the status of an interface on a router, we use a CLI command such as:

R1# show ip interface g0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
  Internet address is 10.10.12.2/24
  Broadcast address is 255.255.255.255

This output is:

• human-readable

• easy for a network engineer to understand

The Same Interface Information in JSON

JSON represents the exact same information, but in a machine-readable format.

Important to understand:

• nothing new is added

• nothing is removed

• only the format changes

{
  "interface": "GigabitEthernet0/1",
  "status": "up",
  "protocol": "up",
  "connection_state": "connected",
  "ip_address": "10.10.12.2",
  "prefix": 24,
  "broadcast_address": "255.255.255.255"
}

JSON organizes the information in a structured way so applications can easily read and interpret it.

JSON does not replace the CLI.
The CLI is designed for humans, while JSON is designed for machines.

"At first, JSON may look unfamiliar".
This is only because we have not yet learned how to read it.

The next section focuses on understanding the structure of JSON, step by step.

To understand JSON, we need to move step by step.

In JSON, the root element can be:

• an object

• or an array

We will start with the most common one: the JSON object.