Software-Defined Networking and Controller-Based Architectures

From Traditional Networks to SDN

Control Plane vs Data Plane

Canonical Definition of SDN

Distributed vs Controller-Based Architectures

Practical Scenario: Rolling Out a New ACL Policy

Cisco DNA Center: Where It Fits

APIs and REST: How Controllers Talk

Simple REST API Call to a Controller

This step gives you a feel for how a script might interact with a controller such as Cisco DNA Center using a REST API. You are not required to memorize syntax, but seeing it once makes exam questions less abstract.

Imagine you want to list all network devices known to the controller. A typical flow is:

1. Authenticate and obtain a token.
2. Use the token in an HTTP GET request to a resource such as `/network-device`.

Below is a simplified Python example using the `requests` library. It is conceptual, not production-ready.

```python

import requests

BASE_URL = "https://dnac.example.com/api/v1"

USERNAME = "admin"

PASSWORD = "Cisco123!"

1. Authenticate and get a token

auth_resp = requests.post(

f"{BASE_URL}/auth/token",

auth=(USERNAME, PASSWORD),

verify=False # do not do this in production

)

authresp.raisefor_status()

token = auth_resp.json()["Token"]

headers = {

"X-Auth-Token": token,

"Content-Type": "application/json"

}

2. Get the list of network devices

devices_resp = requests.get(

f"{BASE_URL}/network-device",

headers=headers,

verify=False

)

devicesresp.raisefor_status()

devices = devices_resp.json()["response"]

for dev in devices:

print(dev["hostname"], dev["managementIpAddress"])

```

Conceptual takeaways:

• You talk to the controller, not directly to every switch.
• You use HTTP methods (POST for auth, GET for data) and URIs.
• The response is JSON you can parse and loop over.

Exam questions may show small JSON snippets or API URLs and ask what they represent or which HTTP method is appropriate.

Thought Exercise: Mapping Old Concepts to SDN

Use this mental exercise to connect earlier topics (ACLs, VLANs, DHCP, wireless security) to SDN and controller-based networking.

Work through these questions in your head or jot short answers:

1. VLANs and Segmentation

You know that "A Virtual Local Area Network (VLAN) is a logical subdivision of a Layer 2 network that groups devices into the same broadcast domain regardless of their physical location."

• In a traditional network, how do you create and assign VLANs to access ports?
• In an SDN campus fabric (like Cisco SD-Access), how might you instead think in terms of “virtual networks” or “groups” that the controller maps to VLANs behind the scenes?

1. ACLs and Policy

• Previously, you placed ACLs on specific interfaces and directions. In a controller-based design, where do you define the intent of the policy?
• Who decides where to enforce it: you, or the controller?

1. DHCP and IP Addressing

Recall: "The Dynamic Host Configuration Protocol (DHCP) automatically assigns IP configuration parameters such as IP address, subnet mask, default gateway, and DNS servers to clients."

• In a traditional network, how do you make sure the right DHCP scope is used for each VLAN?
• With a controller like Cisco DNA Center, how could centralized IP address pool management reduce misconfigurations?

1. Wireless Security

• Think of features like WPA2-Enterprise and guest networks. How might a controller simplify creating consistent SSIDs and security policies across dozens of access points?

Pause and ensure you can explain, in your own words, how the same concepts (VLANs, ACLs, DHCP, wireless security) are still present, but the way you configure and manage them changes with SDN.

Quick Check: SDN and Control/Data Planes

Test your understanding of SDN fundamentals and control/data plane separation.

Quiz: Traditional vs Controller-Based

Another short quiz to reinforce the difference between distributed and controller-based architectures.

Key Term Flashcards: SDN and Controllers

Use these flashcards to solidify core terminology before moving on.

Where SDN Appears in the CCNA Exam (Automation Domain)