Identify the parts of an HTTP response (response code, headers, body)

📘Cisco DevNet Associate (200-901 DEVASC)

---

Overview

When you make a request to a server using HTTP (like a REST API call), the server sends back a response. This response tells you:

1. Whether your request was successful.
2. Extra details about the server or data.
3. The data you requested (if applicable).

An HTTP response has three main parts:

1. Response Code (Status Code)
2. Headers
3. Body

---

1. HTTP Response Code (Status Code)

The response code is a 3-digit number that tells you the result of your request. Think of it as a quick status check from the server.

Common Response Code Classes

Class	Code Range	Meaning	Example Use in IT Environment
1xx	100–199	Informational	Rarely used in APIs; server is processing your request.
2xx	200–299	Success	200 OK → GET request returned data; 201 Created → POST request successfully created a resource.
3xx	300–399	Redirection	301 Moved Permanently → URL changed; API clients need to follow the new URL.
4xx	400–499	Client Error	400 Bad Request → invalid request syntax; 401 Unauthorized → missing authentication; 404 Not Found → resource doesn’t exist.
5xx	500–599	Server Error	500 Internal Server Error → server has a problem; 503 Service Unavailable → server temporarily cannot handle requests.

Key points for the exam:

• The first digit indicates the class (success, error, etc.).
• You will often need to interpret the code to troubleshoot APIs.

---

2. HTTP Headers

Headers are metadata about the response. They are key-value pairs sent before the body. Headers don’t contain the main data, but give important info about it.

Common Headers in IT / APIs

Header	Purpose	Example
Content-Type	Tells the client the format of the data in the body	application/json → the body contains JSON data
Content-Length	Size of the body in bytes	512 → body is 512 bytes
Date	When the response was sent	Tue, 25 Feb 2026 15:30:00 GMT
Server	Information about the server software	nginx/1.24.0
Authorization	Tokens for APIs (if needed)	Bearer <token>
Set-Cookie	Instructs client to store cookies	sessionId=abc123; HttpOnly

Key points for the exam:

• Headers can affect how the client processes the data.
• They are important for authentication, caching, content format, and more.

---

3. HTTP Body

The body is the main content of the response. This is where the server sends the data you requested (if any).

Body Formats

• JSON (most common for REST APIs) {
  “id”: 101,
  “name”: “Device1”,
  “status”: “active”
  }
• XML (less common now, older APIs)
• HTML (web pages)
• Plain text

Body can be empty:

• For some responses like 204 No Content, there is no body, only headers.

Key points for the exam:

• The body contains the actual data your API call requested.
• You need to look at headers like Content-Type to understand how to parse it.

---

Putting It All Together

A full HTTP response might look like this (simplified):

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 85
Date: Tue, 25 Feb 2026 15:30:00 GMT{
  "deviceId": "R1",
  "status": "up",
  "ip": "192.168.1.1"
}

• 200 OK → status code tells the request was successful
• Headers → metadata (type of data, size, server info)
• Body → actual data (device information in JSON)

---

Exam Tips

1. Remember the three parts: Status Code → Headers → Body.
2. Know the status code classes: 2xx = success, 4xx = client error, 5xx = server error.
3. Headers give important instructions about how to read the body or handle the response.
4. Body contains the data; it may be JSON, XML, HTML, or empty.
5. Practice reading HTTP responses in Postman or curl so you can quickly identify each part.

---

This knowledge is essential for troubleshooting APIs and passing the DEVASC exam. Understanding how a server responds lets you fix errors, extract data, and automate tasks using REST APIs.