📘Cisco DevNet Associate (200-901 DEVASC)

1. Introduction to API Styles

An API (Application Programming Interface) allows one software application to communicate with another software application.

In the DevNet Associate exam, you must understand:

Different API architectural styles
How they work
Their characteristics
When they are typically used in IT environments
Their advantages and limitations

The most important styles for the exam are:

REST
RPC
Synchronous APIs
Asynchronous APIs

2. REST (Representational State Transfer)

REST is the most commonly used API style today, especially in web services and cloud platforms.

REST APIs are typically built on:

HTTP protocol
Standard HTTP methods (GET, POST, PUT, DELETE)
JSON format for data exchange

2.1 Key Characteristics of REST

1. Resource-Based

REST is built around resources.

A resource is any object or data that the API manages.

Examples in an IT environment:

A network device
A user account
A VLAN
A virtual machine
A ticket in a ticketing system

Each resource is identified using a URI (Uniform Resource Identifier).

Example:

/devices
/devices/101
/users/55

2. HTTP Methods in REST

REST uses standard HTTP methods:

Method	Purpose
GET	Retrieve data
POST	Create new resource
PUT	Update resource
DELETE	Remove resource

Example (network automation platform):

GET /devices → Get list of devices
POST /devices → Add a new device
PUT /devices/101 → Update device
DELETE /devices/101 → Remove device

3. Stateless

REST is stateless.

This means:

Each request is independent
The server does NOT remember previous requests
All required information must be included in each request

This improves:

Scalability
Performance
Simplicity

4. Data Format

REST commonly uses:

JSON (most common)
XML (less common today)

Example JSON response:

{
  "id": 101,
  "hostname": "router1",
  "status": "active"
}

5. Uses HTTP Status Codes

REST APIs use standard HTTP response codes:

200 OK
201 Created
400 Bad Request
401 Unauthorized
404 Not Found
500 Internal Server Error

Understanding these is important for troubleshooting in the exam.

2.2 Where REST is Used in IT

REST is used in:

Cloud platforms
Network controllers
Monitoring tools
DevOps automation tools
SaaS platforms

Examples:

Cisco Meraki Dashboard API
Cisco DNA Center APIs
GitHub REST API

2.3 Advantages of REST

Simple to understand
Uses standard HTTP
Lightweight
Scalable
Works well over the internet

2.4 Limitations of REST

Sometimes requires multiple requests
No strict standard enforcement
Can be less efficient for complex operations

3. RPC (Remote Procedure Call)

RPC is another API style.

Instead of focusing on resources (like REST), RPC focuses on actions or functions.

It works like calling a function in another system.

3.1 How RPC Works

In RPC:

The client calls a specific method
The server executes that method
The server returns the result

Example (network system):

rebootDevice(deviceID)
getDeviceStatus(deviceID)
createUser(username)

Here, the API is centered around actions, not resources.

3.2 Types of RPC

Common RPC technologies include:

gRPC
XML-RPC
SOAP

SOAP (Simple Object Access Protocol)

Uses XML
Strict structure
Enterprise environments
Strong security features

Often used in:

Financial systems
Enterprise applications

gRPC

Developed by Google
High performance
Uses Protocol Buffers (binary format)
Used in microservices architecture

3.3 RPC Characteristics

Action-based
Usually tightly coupled
Can be faster than REST
Often used internally between services

3.4 RPC vs REST (Exam Comparison)

Feature	REST	RPC
Focus	Resources	Actions/Functions
Protocol	HTTP	Various
Data Format	JSON (usually)	JSON, XML, Binary
Style	Standardized	Implementation-specific
Scalability	High	Depends on implementation

For the exam:

REST = resource-oriented
RPC = function-oriented

4. Synchronous APIs

Synchronous means:

The client:

Sends a request
Waits for response
Does nothing until response is received

This is blocking communication.

4.1 How It Works

Example (IT environment):

A monitoring tool sends request to network controller
It waits for device status
Only after response arrives, it continues processing

4.2 Characteristics

Simple design
Easy to understand
Immediate response
Client waits

4.3 Limitations

Not efficient for long tasks
Can slow down applications
Not good for large-scale event processing

4.4 Common Usage

Most REST APIs
CLI-based API calls
Simple automation scripts

5. Asynchronous APIs

Asynchronous means:

The client:

Sends a request
Does NOT wait
Continues other work
Gets response later

This is non-blocking communication.

5.1 How It Works

Two common methods:

1. Polling

Client checks repeatedly:

GET /task/123/status

2. Webhooks

Server sends notification automatically when ready.

Example:

Network controller finishes device configuration
Sends notification to client system

5.2 Message-Based Asynchronous Systems

Often uses message brokers such as:

Apache Kafka
RabbitMQ

These systems:

Send messages to queues
Process events independently
Enable event-driven architecture

5.3 Characteristics

Non-blocking
Scalable
Good for long-running operations
Good for event-driven systems

5.4 IT Use Cases

Network provisioning tasks
Bulk device configuration
Log processing
Monitoring alerts
Cloud resource deployment

6. Synchronous vs Asynchronous (Exam Comparison)

Feature	Synchronous	Asynchronous
Client waits?	Yes	No
Blocking?	Yes	No
Complexity	Simple	More complex
Performance	Lower for large systems	Better scalability
Good for	Simple tasks	Long tasks, events

Exam Tip:

Immediate response → Synchronous
Background processing → Asynchronous

7. REST vs RPC vs Sync vs Async (Important Exam Concept)

REST and RPC are architectural styles.

Synchronous and Asynchronous are communication patterns.

You can combine them:

REST + Synchronous (most common)
REST + Asynchronous (long-running task APIs)
RPC + Synchronous
RPC + Asynchronous (microservices with message brokers)

The exam may test whether you understand this difference.

8. Quick Exam Summary

You must remember:

REST

Resource-based
Uses HTTP methods
Stateless
JSON format
Most common in modern APIs

RPC

Action/function-based
Calls remote method
Can use SOAP or gRPC
Often used in internal systems

Synchronous

Client waits
Blocking
Simple

Asynchronous

Client does not wait
Event-driven
Better for scaling
Uses polling or webhooks

9. Final Exam Preparation Tips

For DevNet Associate:

Be able to:

Identify whether an API is REST or RPC
Recognize synchronous vs asynchronous behavior
Understand where each style is used
Compare advantages and disadvantages
Understand event-driven systems
Recognize message brokers
Understand polling vs webhooks

If you understand:

Resource vs Action
Blocking vs Non-blocking
HTTP vs method calls

You are well prepared for this section of the exam.