Troubleshoot a problem given the HTTP response code, request and API documentation

📘Cisco DevNet Associate (200-901 DEVASC)

---

When working with APIs (Application Programming Interfaces), sometimes things don’t work as expected. To troubleshoot effectively, you need to understand HTTP response codes, how requests are made, and how to read API documentation.

---

1. What is an HTTP Request and Response?

In API communication:

• HTTP Request: This is your message to the server asking it to do something. It contains:
  • Method (what you want to do, like GET, POST, PUT, DELETE)
  • URL/Endpoint (where you are sending the request)
  • Headers (extra info like authentication, content type)
  • Body (data you want to send, usually for POST or PUT requests)
• HTTP Response: This is the server’s reply. It contains:
  • Status Code (tells you if the request worked or failed)
  • Headers (additional info about the response)
  • Body (data returned from the server, like JSON)

Example:
You send a GET request to a server to fetch user information. The server responds with a status code 200 OK and the user’s details in JSON format.

---

2. HTTP Response Codes

HTTP response codes are numbers that tell you what happened with your request. Knowing them is key to troubleshooting.

Categories of HTTP Codes:

1. 1xx – Informational
   • Rarely seen in APIs. It means the request is being processed.
2. 2xx – Success
   • 200 OK – Request succeeded; response contains the requested data.
   • 201 Created – Resource successfully created (usually after POST).
   • 204 No Content – Request succeeded but no data returned (often after DELETE).
3. 3xx – Redirection
   • 301 Moved Permanently – Resource has moved to a new URL.
   • 302 Found / 307 Temporary Redirect – Resource temporarily moved.
4. 4xx – Client Error (your request has an issue)
   • 400 Bad Request – The request syntax is wrong or missing data.
   • 401 Unauthorized – Missing or invalid authentication.
   • 403 Forbidden – You don’t have permission to access this resource.
   • 404 Not Found – Endpoint or resource doesn’t exist.
   • 409 Conflict – Trying to create something that already exists.
5. 5xx – Server Error (server has an issue)
   • 500 Internal Server Error – Generic server problem.
   • 502 Bad Gateway / 503 Service Unavailable – Server is down or overloaded.

Tip for Exam: Remember, 4xx = client problem, 5xx = server problem. That helps narrow troubleshooting quickly.

---

3. How to Troubleshoot Using HTTP Response Codes

When an API request fails, these steps help:

1. Check the HTTP response code
   • Identify the category of the problem (success, client error, server error).
2. Examine the response body and headers
   • Some APIs return detailed error messages in JSON.
   • Example: { "error": "User not found", "code": 404 }
3. Check your request
   • Verify the method (GET, POST, etc.) matches API documentation.
   • Check URL/endpoint spelling.
   • Check headers (authentication, content type).
   • Check body/payload if sending data.
4. Consult the API documentation
   • Documentation shows required parameters, valid values, authentication methods.
   • Compare your request with the examples in the documentation.
5. Correct the issue
   • Fix authentication → resolve 401 Unauthorized.
   • Correct payload → fix 400 Bad Request.
   • Use correct endpoint → fix 404 Not Found.

---

4. Real IT Examples

Example 1: 401 Unauthorized

• You try to fetch a list of network devices from a management API.
• Response: 401 Unauthorized.
• Check: Are you using the correct API key or token in the headers?
• Fix: Add or correct authentication in your request header: Authorization: Bearer <your_token_here>

Example 2: 400 Bad Request

• You send a POST request to create a new user but miss the "email" field.
• Response: 400 Bad Request.
• Check API docs: "email" is required.
• Fix: Include "email" in the JSON body.

Example 3: 404 Not Found

• You request /devices/12345 but get 404.
• Check: Does device ID 12345 exist?
• Fix: Correct the endpoint or ID.

---

5. Using API Documentation Effectively

API documentation is your roadmap. Always check:

• Endpoints – Correct URLs for different actions.
• Methods – Use the right HTTP method (GET, POST, PUT, DELETE).
• Headers – Required authentication, content type.
• Request Body – Required fields, correct format (JSON, XML).
• Response Codes – What each code means for that endpoint.
• Examples – Copy working examples for testing your request.

---

6. Exam Tip: Troubleshooting Scenario Approach

When the exam gives you a problem with HTTP response codes:

1. Identify the status code.
2. Determine if it’s a client or server issue.
3. Check request method, headers, and body.
4. Compare with API documentation.
5. Choose the most likely fix based on the code and your check.

---

✅ Key Takeaways

• HTTP status codes tell you what went wrong.
• 4xx → client issues; 5xx → server issues.
• Always check request correctness: method, URL, headers, and body.
• API documentation is essential for troubleshooting.
• Use response body messages to guide fixes.

---

This approach will help your students diagnose and solve API problems efficiently, which is exactly what the exam tests.