200-301 Automation and Programmability

Automation and Programmability Detailed Explanation

Automation and programmability are essential for modern networking, enabling faster deployments, reduced human error, and centralized management.

Part 1: Software-Defined Networking (SDN)

6.1.1 What is SDN?

SDN stands for Software-Defined Networking, a modern approach to networking that separates:

1. Control Plane: Where decisions are made about how traffic is handled.
   • Example: Determining the best path for data packets.
2. Data Plane: Where traffic is forwarded based on the decisions from the control plane.
   • Example: Actual packet forwarding through switches and routers.

In traditional networks, both planes are integrated into devices, making management complex. SDN separates these planes, allowing for centralized control.

6.1.2 Benefits of SDN

1. Centralized Management:

   • Control the entire network from a central controller, like a "command center."
   • Example: Configuring multiple switches simultaneously from one location.

2. Dynamic Network Configurations:

   • Quickly adapt to changes like adding new devices or applications.
   • Example: Automatically rerouting traffic during link failure.

3. Improved Scalability:

   • Easily manage and scale large networks without manual reconfiguration.

4. Programmability:

   • Use APIs to automate tasks, reducing manual effort and errors.

6.1.3 How SDN Works

1. Applications:

   • Network management tools or custom applications that use SDN to make decisions.
   • Example: A traffic monitoring app that reroutes congested paths.

2. Controller:

   • Centralized brain of the network, making decisions and sending instructions to devices.
   • Example: OpenDaylight, Cisco APIC.

3. Network Devices:

   • Routers, switches, or firewalls that handle actual data forwarding based on controller instructions.

6.1.4 SDN Example

Suppose you have three switches, and you want to configure a VLAN across all of them. Without SDN, you'd configure each switch manually. With SDN, you can:

1. Use a centralized controller.
2. Define the VLAN once in the controller.
3. Automatically apply the configuration to all switches.

Part 2: Network Automation Tools

6.2.1 What is Network Automation?

Network automation uses tools or scripts to perform tasks like device configuration, monitoring, and troubleshooting without manual intervention.

6.2.2 Popular Network Automation Tools

1. Ansible:

   • Agentless: Does not require software installation on devices.
   • Uses YAML Playbooks: Human-readable scripts for configuration.

   Ansible Example:
   Configure a VLAN on a Cisco switch.

   - name: Configure a switch
    hosts: switches
    tasks:
      - name: Configure VLAN
        ios_config:
          lines:
            - vlan 10
            - name Sales
   

   Steps:

   1. Define the hosts file with the switch's IP addresses.

   2. Run the playbook:

      ansible-playbook configure_vlan.yaml
      

2. Python Scripting with Netmiko:

   • What is Netmiko?: A Python library for SSH-based automation.

   • Example: Retrieve the interface status of a Cisco router.

     from netmiko import ConnectHandler
     
     device = {
        "device_type": "cisco_ios",
        "ip": "192.168.1.1",
        "username": "admin",
        "password": "cisco123"
     }
     
     net_connect = ConnectHandler(**device)
     output = net_connect.send_command("show ip interface brief")
     print(output)
     

Steps:

1. Install Netmiko:

   pip install netmiko
   

2. Run the script to fetch interface details.

Part 3: REST APIs

6.3.1 What is a REST API?

REST (Representational State Transfer) APIs allow network devices to be programmatically managed using HTTP methods like:

• GET: Retrieve information.
• POST: Add new data or configurations.
• PUT: Update existing configurations.
• DELETE: Remove configurations.

REST APIs are commonly used in SDN controllers and modern network devices.

6.3.2 Why Use REST APIs?

1. Automation:
   • Perform tasks programmatically, reducing manual effort.
2. Integration:
   • Combine network management with other IT systems (e.g., monitoring tools).
3. Flexibility:
   • Control devices from scripts or applications.

6.3.3 Example of a REST API Call

Suppose you want to retrieve the interface status of a router using a REST API.

GET Request Example:

1. Use the following HTTP request:

   GET http://router/api/interfaces
   

2. Example Python Script:

   import requests
   
   url = "http://192.168.1.1/api/interfaces"
   headers = {
      "Content-Type": "application/json",
      "Authorization": "Bearer YOUR_ACCESS_TOKEN"
   }
   
   response = requests.get(url, headers=headers)
   print(response.json())
   

   Steps:

   1. Replace YOUR_ACCESS_TOKEN with the actual API token.
   2. Run the script to get the interface details.

6.3.4 Verifying REST API Connectivity

• Test API Access: Use tools like Postman to manually send API requests.

• Check Device API Settings:

  show restconf
  

Automation and Programmability (Additional Content)

1. Southbound Protocol – OpenFlow

OpenFlow is one of the first and most well-known southbound protocols in SDN architecture. It defines how the SDN controller communicates with network devices (e.g., switches, routers) to install forwarding rules.

Key Characteristics:

• Used by SDN controllers to direct packet forwarding decisions on OpenFlow-compatible switches.

• The controller sends flow entries to the devices that specify how to handle traffic.

• Enables centralized control and dynamic traffic management.

Example Use Case:

In an SDN network, when a switch receives a packet with no matching rule, it forwards the packet to the controller for instructions (packet-in message). The controller then responds with a flow-mod message to define future handling of similar packets.

2. RESTCONF and NETCONF

2.1 NETCONF (Network Configuration Protocol)

• XML-based protocol used to retrieve and edit configuration data on network devices.

• Built on top of SSH.

• Works well with YANG data models to structure configuration data.

2.2 RESTCONF

• A RESTful API (HTTP-based) interface that exposes YANG-modeled configuration and state data.

• Supported on Cisco IOS XE and other modern devices.

• Cisco’s implementation of RESTful network management.

Comparison:

Feature	NETCONF	RESTCONF
Format	XML	JSON or XML
Transport	SSH	HTTPS (HTTP REST interface)
Data Model	YANG	YANG
Use Case	Precise config retrieval	Web-friendly API access

3. JSON Data Format Overview

JSON (JavaScript Object Notation) is a lightweight, human-readable format used for data interchange, especially in REST APIs.

Basic Example:

{
  "interface": {
    "name": "GigabitEthernet0/1",
    "enabled": true,
    "ip": {
      "address": "192.168.1.1",
      "netmask": "255.255.255.0"
    }
  }
}

Why JSON in Networking?

• REST APIs return data in JSON for easy parsing and readability.

• Widely supported by Python, JavaScript, and network automation tools.

4. API Authentication Mechanisms

APIs require secure access control. CCNA candidates should recognize the following basic authentication methods:

4.1 Token-Based Authentication

• The client authenticates once and receives a token.

• All subsequent API calls include the token in the Authorization header.

Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

4.2 Basic Authentication

• The username and password are base64-encoded and sent with every request.

Authorization: Basic YWRtaW46Y2lzY28=

Security Note: Basic Auth should always be used with HTTPS to protect credentials.

5. Automation Tools: Ansible vs. Python

Both Ansible and Python scripting are used in network automation but serve different purposes and styles.

5.1 Ansible (Declarative Automation)

• Agentless: Uses SSH, no software needed on devices.

• Uses YAML playbooks to describe desired configurations.

• Best suited for bulk device configuration and repetitive tasks.

Example Playbook:

- name: Configure VLAN
  hosts: switches
  tasks:
    - name: Create VLAN 10
      ios_config:
        lines:
          - vlan 10
          - name Sales

5.2 Python with Netmiko or NAPALM (Imperative Automation)

• Offers fine-grained logic and control.

• Suitable for custom workflows, decision-making, and error handling.

• Requires programming knowledge but provides more flexibility.

Example (Using Netmiko):

from netmiko import ConnectHandler

device = {
  "device_type": "cisco_ios",
  "ip": "192.168.1.1",
  "username": "admin",
  "password": "cisco123"
}

net_connect = ConnectHandler(**device)
output = net_connect.send_command("show ip interface brief")
print(output)

Comparison Summary:

Tool	Approach	Use Case	Best For
Ansible	Declarative	Large-scale deployments	Simplifying repetitive tasks
Python	Imperative	Custom logic and scripting	Advanced, conditional workflows

Summary of Key Additions

Topic	What You Should Know for CCNA
OpenFlow	Southbound SDN protocol used between controller and devices
RESTCONF / NETCONF	Cisco-supported config protocols; RESTCONF is HTTP-based
JSON	REST APIs return data in JSON; know syntax and usage
API Authentication	Token-based and Basic Auth – secure access to APIs
Ansible vs Python	Know when to use each tool; Ansible = simple bulk ops, Python = custom logic