Extracted from the original export. Diagrams and some formatting appear in the notes above.

Day 61 - REST API
Thursday, September 10, 2026 11:16 AM
REST API Info
An API is a software interface that allows two applications to communicate with each other.
• APIs are essential not just for network automation, but for all kinds of applications.
• IN SDN architecture, APIs are used to communicate between apps and the SDN Controller (via the NBI), and
between the SDN Controller and the network devices (via the SBI).
• The NBI typically uses REST APIs
• Netconf and Restconf are popular Southbound APIs.
CRUD
CRUD (Create, Read, Update, Delete) refers to the operations we perform using REST APIs.
1. Create
○ Create operations are used to create new variables and set their initial values.
○ Example: Create variable “ip_address” and set the value to “10.1.1.1”
2. Read
○ Read operations are used to retrieve the value of a variable.
○ Example: What is the value of variable “ip_address”?
3. Update
○ Update operations are used to change the value of variable.
○ Example: Change the value of variable “ip_address” to “10.2.3.4”
4. Delete
○ Delete operations are used to delete variables.
○ Example: Delete variables “ip_address”.
• HTTP uses verbs (aka. methods) to map these CRUD operations.
• REST APIs typically use HTTP.
Purpose CRUD Operation HTTP Verb
Create new variable Create POST
Retrieve value of a value Read GET
Change the value of variable Update PUT, PATCH
Delete variable Delete DELETE
HTTP Request
When an HTTP client sends a request to an HTTP server, the HTTP header includes information like this:
• An HTTP Verb (ie. GET).
• A URI (Uniform Resource Identifier), indicating the resource it is trying to access.
HTTP Request Example
• A URI consists of three different parts
1. Scheme
2. Authority
3. Paths
• Example: https://sandboxdnac.cisco.com/dna/intent/api/v1/network-device
○ Scheme: https
○ Authority: sandboxdnac.cisco.com
○ Paths: dna/intent/api/v1/network-device
HTTP Request - Headers
• HTTP request can include additional headers which pass additional information to the server.
Example HTTP Request with extra headers
• An example would an Accept header, which informs the server about the type(s) of data that can be sent back
to the client.
• When a REST client makes an API call (request) to a REST server, it will send an HTTP request like the one above.
• REST APIs don’t have to use HTTP specifically for communication, although HTTP is the most common choice.
HTTP Response
• The server’s response will include a status code indicating the request succeeded or failed, as well as the other
details.
• The first digit indicates the class of the response:
1. 1xx Informational
§ The request was received, continuing process.
2. 2xx Successful
§ The request was successfully received, understood, and accepted.
3. 3xx Redirection
§ Further action needs to be taken in order to complete the request.
4. 4xx Client Error
§ The request contains bad syntax or cannot be fulfilled.
5. 5xx Server Error
§ The server failed to fulfill an apparently valid request.
HTTP Request & Response Example (1)
HTTP Response - Example Codes
1. 1xx Information
○ 102 Processing:
§ Indicates that the server has received the request and is processing it, but the response is not yet
available.
2. 2xx Successful
○ 200 OK
§ Indicates that the request succeeded.
○ 201 Created
§ Indicates that the request succeeded and a new resource was created (ie. in response to POST)
3. 3xx Redirection
○ 301 Moved Permanently
§ Permanently indicates that the requested resource has been moved, and the server indicates its
new location.
4. 4xx Client Error
○ 403 Unauthorized
§ Means the client must authenticate to get a response.
○ 404 Not Found
§ Means the requested resource was not found.
5. 5xx Server Error
○ 500 Internal Server Error
§ Means the server encountered something unexpected that it doesn’t know how to handle.
REST
REST stands for Representational State Transfer.
• REST APIs are also known as REST-based APIs OR RESTful APIs
• REST isn’t a specific API. Instead, it describes a set of rules about how the API should work.
• The six constraints of RESTful architecture are:
1. Uniform Interface
2. Client-server
3. Stateless
4. Cacheable or non-cacheable
5. Layered system
6. Code-on-demand
REST - Client-server
REST APIs use a client-server architecture.
• The client uses API calls (HTTP Requests) to access the resources on the server.
• The separation between the client and server means they can both change and evolve independently of each
other.
○ Therefore, when the client application changes or the server application changes, the interface between
them must NOT break.
HTTP Request & Response Example (2)
REST - Stateless
REST APIs exchanges are stateless
• This means that each API exchange is a separate event, independent of all past exchanges between the client
and server.
• The server does not store information about previous requests from the client to determine how it should
respond to new requests.
• If authentication is required, this means that the client must authenticate with the server for each request it
makes.
• TCP is an example of a stateful protocol.
• UDP is an example of a stateless protocol.
REST APIs and TCP - Stateful and Stateless
○ Although REST APIs use HTTP, which uses TCP (stateful) as its Layer 4 protocol, HTTP and REST APIs
themselves aren’t stateful. The functions of each layer are separate.
REST - Cacheable or Non-Cacheable
REST APIs must support caching of data.
• Caching refers to storing data for future use.
• Not all resources have to be cacheable, but cacheable resources MUST be declared as cacheable.

Day 61 - REST API
Thursday, September 10, 2026 11:16 AM
REST API Info
An API is a software interface that allows two applications to communicate with each other.
• APIs are essential not just for network automation, but for all kinds of applications.
• IN SDN architecture, APIs are used to communicate between apps and the SDN Controller (via the NBI), and
between the SDN Controller and the network devices (via the SBI).
• The NBI typically uses REST APIs
• Netconf and Restconf are popular Southbound APIs.
CRUD
CRUD (Create, Read, Update, Delete) refers to the operations we perform using REST APIs.
1. Create
○ Create operations are used to create new variables and set their initial values.
○ Example: Create variable “ip_address” and set the value to “10.1.1.1”
2. Read
○ Read operations are used to retrieve the value of a variable.
○ Example: What is the value of variable “ip_address”?
3. Update
○ Update operations are used to change the value of variable.
○ Example: Change the value of variable “ip_address” to “10.2.3.4”
4. Delete
○ Delete operations are used to delete variables.
○ Example: Delete variables “ip_address”.
• HTTP uses verbs (aka. methods) to map these CRUD operations.
• REST APIs typically use HTTP.
Purpose CRUD Operation HTTP Verb
Create new variable Create POST
Retrieve value of a value Read GET
Change the value of variable Update PUT, PATCH
Delete variable Delete DELETE
HTTP Request
When an HTTP client sends a request to an HTTP server, the HTTP header includes information like this:
• An HTTP Verb (ie. GET).
• A URI (Uniform Resource Identifier), indicating the resource it is trying to access.
HTTP Request Example
• A URI consists of three different parts
1. Scheme
2. Authority
3. Paths
• Example: https://sandboxdnac.cisco.com/dna/intent/api/v1/network-device
○ Scheme: https
○ Authority: sandboxdnac.cisco.com
○ Paths: dna/intent/api/v1/network-device
HTTP Request - Headers
• HTTP request can include additional headers which pass additional information to the server.
Example HTTP Request with extra headers
• An example would an Accept header, which informs the server about the type(s) of data that can be sent back
to the client.
• When a REST client makes an API call (request) to a REST server, it will send an HTTP request like the one above.
• REST APIs don’t have to use HTTP specifically for communication, although HTTP is the most common choice.
HTTP Response
• The server’s response will include a status code indicating the request succeeded or failed, as well as the other
details.
• The first digit indicates the class of the response:
1. 1xx Informational
§ The request was received, continuing process.
2. 2xx Successful
§ The request was successfully received, understood, and accepted.
3. 3xx Redirection
§ Further action needs to be taken in order to complete the request.
4. 4xx Client Error
§ The request contains bad syntax or cannot be fulfilled.
5. 5xx Server Error
§ The server failed to fulfill an apparently valid request.
HTTP Request & Response Example (1)
HTTP Response - Example Codes
1. 1xx Information
○ 102 Processing:
§ Indicates that the server has received the request and is processing it, but the response is not yet
available.
2. 2xx Successful
○ 200 OK
§ Indicates that the request succeeded.
○ 201 Created
§ Indicates that the request succeeded and a new resource was created (ie. in response to POST)
3. 3xx Redirection
○ 301 Moved Permanently
§ Permanently indicates that the requested resource has been moved, and the server indicates its
new location.
4. 4xx Client Error
○ 403 Unauthorized
§ Means the client must authenticate to get a response.
○ 404 Not Found
§ Means the requested resource was not found.
5. 5xx Server Error
○ 500 Internal Server Error
§ Means the server encountered something unexpected that it doesn’t know how to handle.
REST
REST stands for Representational State Transfer.
• REST APIs are also known as REST-based APIs OR RESTful APIs
• REST isn’t a specific API. Instead, it describes a set of rules about how the API should work.
• The six constraints of RESTful architecture are:
1. Uniform Interface
2. Client-server
3. Stateless
4. Cacheable or non-cacheable
5. Layered system
6. Code-on-demand
REST - Client-server
REST APIs use a client-server architecture.
• The client uses API calls (HTTP Requests) to access the resources on the server.
• The separation between the client and server means they can both change and evolve independently of each
other.
○ Therefore, when the client application changes or the server application changes, the interface between
them must NOT break.
HTTP Request & Response Example (2)
REST - Stateless
REST APIs exchanges are stateless
• This means that each API exchange is a separate event, independent of all past exchanges between the client
and server.
• The server does not store information about previous requests from the client to determine how it should
respond to new requests.
• If authentication is required, this means that the client must authenticate with the server for each request it
makes.
• TCP is an example of a stateful protocol.
• UDP is an example of a stateless protocol.
REST APIs and TCP - Stateful and Stateless
○ Although REST APIs use HTTP, which uses TCP (stateful) as its Layer 4 protocol, HTTP and REST APIs
themselves aren’t stateful. The functions of each layer are separate.
REST - Cacheable or Non-Cacheable
REST APIs must support caching of data.
• Caching refers to storing data for future use.
• Not all resources have to be cacheable, but cacheable resources MUST be declared as cacheable.

Day 61 - REST API
Thursday, September 10, 2026 11:16 AM
REST API Info
An API is a software interface that allows two applications to communicate with each other.
• APIs are essential not just for network automation, but for all kinds of applications.
• IN SDN architecture, APIs are used to communicate between apps and the SDN Controller (via the NBI), and
between the SDN Controller and the network devices (via the SBI).
• The NBI typically uses REST APIs
• Netconf and Restconf are popular Southbound APIs.
CRUD
CRUD (Create, Read, Update, Delete) refers to the operations we perform using REST APIs.
1. Create
○ Create operations are used to create new variables and set their initial values.
○ Example: Create variable “ip_address” and set the value to “10.1.1.1”
2. Read
○ Read operations are used to retrieve the value of a variable.
○ Example: What is the value of variable “ip_address”?
3. Update
○ Update operations are used to change the value of variable.
○ Example: Change the value of variable “ip_address” to “10.2.3.4”
4. Delete
○ Delete operations are used to delete variables.
○ Example: Delete variables “ip_address”.
• HTTP uses verbs (aka. methods) to map these CRUD operations.
• REST APIs typically use HTTP.
Purpose CRUD Operation HTTP Verb
Create new variable Create POST
Retrieve value of a value Read GET
Change the value of variable Update PUT, PATCH
Delete variable Delete DELETE
HTTP Request
When an HTTP client sends a request to an HTTP server, the HTTP header includes information like this:
• An HTTP Verb (ie. GET).
• A URI (Uniform Resource Identifier), indicating the resource it is trying to access.
HTTP Request Example
• A URI consists of three different parts
1. Scheme
2. Authority
3. Paths
• Example: https://sandboxdnac.cisco.com/dna/intent/api/v1/network-device
○ Scheme: https
○ Authority: sandboxdnac.cisco.com
○ Paths: dna/intent/api/v1/network-device
HTTP Request - Headers
• HTTP request can include additional headers which pass additional information to the server.
Example HTTP Request with extra headers
• An example would an Accept header, which informs the server about the type(s) of data that can be sent back
to the client.
• When a REST client makes an API call (request) to a REST server, it will send an HTTP request like the one above.
• REST APIs don’t have to use HTTP specifically for communication, although HTTP is the most common choice.
HTTP Response
• The server’s response will include a status code indicating the request succeeded or failed, as well as the other
details.
• The first digit indicates the class of the response:
1. 1xx Informational
§ The request was received, continuing process.
2. 2xx Successful
§ The request was successfully received, understood, and accepted.
3. 3xx Redirection
§ Further action needs to be taken in order to complete the request.
4. 4xx Client Error
§ The request contains bad syntax or cannot be fulfilled.
5. 5xx Server Error
§ The server failed to fulfill an apparently valid request.
HTTP Request & Response Example (1)
HTTP Response - Example Codes
1. 1xx Information
○ 102 Processing:
§ Indicates that the server has received the request and is processing it, but the response is not yet
available.
2. 2xx Successful
○ 200 OK
§ Indicates that the request succeeded.
○ 201 Created
§ Indicates that the request succeeded and a new resource was created (ie. in response to POST)
3. 3xx Redirection
○ 301 Moved Permanently
§ Permanently indicates that the requested resource has been moved, and the server indicates its
new location.
4. 4xx Client Error
○ 403 Unauthorized
§ Means the client must authenticate to get a response.
○ 404 Not Found
§ Means the requested resource was not found.
5. 5xx Server Error
○ 500 Internal Server Error
§ Means the server encountered something unexpected that it doesn’t know how to handle.
REST
REST stands for Representational State Transfer.
• REST APIs are also known as REST-based APIs OR RESTful APIs
• REST isn’t a specific API. Instead, it describes a set of rules about how the API should work.
• The six constraints of RESTful architecture are:
1. Uniform Interface
2. Client-server
3. Stateless
4. Cacheable or non-cacheable
5. Layered system
6. Code-on-demand
REST - Client-server
REST APIs use a client-server architecture.
• The client uses API calls (HTTP Requests) to access the resources on the server.
• The separation between the client and server means they can both change and evolve independently of each
other.
○ Therefore, when the client application changes or the server application changes, the interface between
them must NOT break.
HTTP Request & Response Example (2)
REST - Stateless
REST APIs exchanges are stateless
• This means that each API exchange is a separate event, independent of all past exchanges between the client
and server.
• The server does not store information about previous requests from the client to determine how it should
respond to new requests.
• If authentication is required, this means that the client must authenticate with the server for each request it
makes.
• TCP is an example of a stateful protocol.
• UDP is an example of a stateless protocol.
REST APIs and TCP - Stateful and Stateless
○ Although REST APIs use HTTP, which uses TCP (stateful) as its Layer 4 protocol, HTTP and REST APIs
themselves aren’t stateful. The functions of each layer are separate.
REST - Cacheable or Non-Cacheable
REST APIs must support caching of data.
• Caching refers to storing data for future use.
• Not all resources have to be cacheable, but cacheable resources MUST be declared as cacheable.