Home > Articles > Automation


Chapter Description

This sample chapter from Cisco Certified DevNet Professional DEVCOR 350-901 Official Cert Guide maps to the second part of the Developing Applications Using Cisco Core Platforms and APIs v1.0 (350-901) Exam Blueprint Section 5.0, ''Infrastructure and Automation.''

Software-Defined Networking (SDN)

The catalyst for software-defined networking is largely attributed to Stanford University’s Clean Slate Program in 2008. Cisco was a sponsor of this project, which reimagined what a new Internet would look like if we set aside conventional norms of traditional networks and worked from a clean slate. It was difficult to develop next-generation routing or connectivity protocols if the equipment available was purposely programmed to follow the original conventions. Programmable logic arrays (PLAs) were pretty expensive to test theories, so a more software-based approach was proposed.

What Is SDN and Network Programmability?


Definitions of SDN and network programmability varied among network IT vendors, but some points were generally agreed upon. As illustrated in Figure 10-10, SDN is

Figure 10.10

Figure 10.10 The SDN Concept

  • An approach and architecture in networking where control and data planes are decoupled, and intelligence and state are logically centralized

  • An enabling technology where the underlying network infrastructure is abstracted from the applications (network virtualization)

  • A concept that leverages programmatic interfaces to enable external systems to influence network provisioning, control, and operations

Although all of these definitions were exciting and transformative, the last item of leveraging programmatic interfaces appeals mostly to the network programming crowd. The last item also enables us to influence the first two through provisioning and monitoring network assets.

In my talks at CiscoLive, I would share that SDN was

  • An approach to network transformation*

  • Empowering alternative, nontraditional entities to influence network design and operations

  • Impacting the networking industry, challenging the way we think about engineering, implementing, and managing networks

  • Providing new methods to interact with equipment and services via controllers and APIs

  • Normalizing the interface with equipment and services

  • Enabling high-scale, rapid network and service provisioning and management

  • Providing a catalyst for traditional route/switch engineers to branch out


So, why the asterisk next to an approach to network transformation? Well, it wasn’t the first attempt at network transformation. If we consider separation of the control plane and data plane, we can look no further than earlier technologies, such as SS7, ATM LANE, the wireless LAN controller, and GMPLS. If we were considering network overlays/underlays and encapsulation, the earlier examples were MPLS, VPLS, VPN, GRE Tunnels, and LISP. Finally, if our consideration was management and programmatic interfaces, we had SNMP, NETCONF and EEM. Nonetheless, SDN was a transformative pursuit.

Nontraditional Entities

What about those nontraditional entities influencing the network? As new programmatic interfaces were purposely engineered into the devices and controllers, a new wave of network programmers joined the environment. Although traditional network engineers skilled up to learn programming (and that may be you, reading this book!), some programmers who had little prior networking experience decided to try their hand at programming a network. Or the programmers decided it was in their best interests to configure an underpinning network for their application themselves, rather than parsing the work out to a network provisioning team.

Regardless of the source of interaction with the network, it is imperative that the new interfaces, telemetry, and instrumentation be secured with the same, if not more, scrutiny as the legacy functions. The security policies can serve to protect the network from unintentional harm by people who don’t have deep experience with the technology and from the intentional harm of bad actors.

Industry Impact

The impact to the network industry with operations and engineering was greatly influenced by control plane and data plane separation and the development of centralized controllers. The network management teams would no longer work as hard to treat each network asset as an atomic unit but could manage a network en masse through the controller. One touchpoint for provisioning and monitoring of all these devices! The ACI APIC controller is acknowledged as one of the first examples of an SDN controller, as seen in Figure 10-11. It was able to automatically detect, register, and configure Cisco Nexus 9000 series switches in a data center fabric.

Figure 10.11

Figure 10.11 Cisco ACI Architecture with APIC Controllers

New Methods

With respect to new methods, protocols, and interfaces to managed assets, APIs became more prolific with the SDN approach. Early supporting devices extended a style of REST-like interface and then more fully adopted the model. First NETCONF and then RESTCONF became the desired norm. Centralized controllers, like the wireless LAN controller, ACI’s APIC controller, Meraki, and others, prove the operational efficiency of aggregating the monitoring and provisioning of fabrics of devices. This model has coaxed the question “What else can we centralize?”


SDN’s impact on network normalization is reflected in the increasingly standardized interfaces. While SNMP had some utility, SDN provided a fresh opportunity to build and use newer management technologies that had security at their core, not just a “bolt-on” consideration. Although the first API experiences felt a bit like the Wild Wild West, the Swagger project started to define a common interface description language to REST APIs. Swagger has since morphed into the OpenAPI initiative, and specification greatly simplifies API development and documentation tasks.

Enabling Operations

Network operations, service provisioning, and management were influenced with SDN through the new interfaces, their standardization, and programmatic fundamentals. Instead of relying on manual CLI methods, operators began to rely on their growing knowledge base of REST API methods and sample scripts in growing their operational awareness and ability to respond and influence network functions.

Besides the REST API, other influences include gRPC Network Management Interface (gNMI), OpenConfig, NETCONF, RESTCONF, YANG, time-series databases, AMQP pub-sub architectures, and many others.

Enabling Career Options

Finally, SDN provided traditional network engineers an opportunity to extend their skills with new network programming expertise. The traditional network engineer with years of domain experience could apply that knowledge in an impactful way with these programmatic interfaces. They could deploy more services at scale, with fewer errors and more quickly.

How impactful could SDN be? Let’s consider the early days of IP telephony: it didn’t ramp up as quickly as desired. On one side there were the traditional “tip-ring telco” team members; on the other side was the new “packet-switch” team. IP telephony technology was slow to gain momentum because few individuals crossed the aisle to learn the other side and become change and translation agents for the greater good. When people started to understand and share the nuanced discipline of the other side, then SDN started to make strides.

Network programmability is in that same transition: there are strong network engineers who understand their tradition route/switch technology. Likewise, there are very strong software developers who understand how to build apps and interact with systems; they just don’t have the network domain expertise. As network engineers skill up with the automation and network programming discipline, they bring their experience of networks with them. So, let’s do IT!

Use Cases and Problems Solved with SDN

SDN aimed to address several use cases. The research and academic communities were looking for ways to create experimental network algorithms and technologies. The hope was to turn these into new protocols, standards, and products. Because existing products closely adhered to well-defined routing protocol specifications, SDN was to help separate the current norms from new, experimental concepts.

The massively scalable data center community appreciated SDN for the ability to separate the control plane from the data plane and use APIs to provide deep insight into network traffic. Cloud providers drew upon SDN for automated provisioning and programmable network overlays. Service providers aligned to policy-based control and analytics to optimize and monetize service delivery. Enterprise networks latched onto SDN’s capability to virtualize workloads, provide network segmentation, and orchestrate security profiles.

Nearly all segments realized the benefits of automation and programmability with SDN:

  • Centralized configuration, management control, and monitoring of network devices (physical or virtual)

  • The capability to override traditional forwarding algorithms to suit unique business or technical needs

  • The capability of external applications or systems to influence network provisioning and operation

  • Rapid and scalable deployment of network services with lifecycle management

Several protocols and solutions contributed to the rise of SDN. See Table 10-4 for examples.


Table 10-4 Contributing Protocols and Solutions to SDN





Layer-2 programmable forwarding protocol and specification for switch manufacturing


Interface to Routing System

Layer-3 programmable protocol to the routing information base (RIB); allowed manipulation and creation of new routing metrics


Path Computation Element Protocol

L3 protocol capable of computing a network path or route based on a network graph and applying computational constraints


BGP Link-State / Flow Spec

The ability to gather IGP topology of the network and export to a central SDN controller or alternative method to remotely triggered black hole filtering useful for DDoS mitigation


Hypervisor technology for virtualization of workloads


Open Management Infrastructure

Open-source Common Information Model with intent to normalize management


Agent-based configuration management solution embedded in devices (later updated to agentless)


Agentless configuration management solution


Network Configuration standard

IETF working group specification normalizing configuration across vendors using XML schemas (later updated with YANG)


Data Modeling Language

Data modeling language for defining IT technologies and services

Overview of Network Controllers

One of the main benefits of SDN was the notion of control plane and data plane separation. You can think of the control plane as the brains of the network: it makes forwarding decisions based on interactions with adjacent devices and their forwarding protocols. The data plane is the muscle, acting on the forwarding decisions programmed into it. Routing protocols like OSPF and BGP operate in the control plane. A link aggregation protocol like LACP or the MAC address table would be representative of the data plane.

The first traditional networks combined the functionality of the control plane/data plane into the same device. Each device acted autonomously, creating and executing its own forwarding decisions. With the advent of SDN, the notion of centralizing that brain function into one control unit yet keeping the data plane function at the managed device was the new architectural goal. These centralized controllers aggregated the monitoring and management function. They oftentimes also provided that centralized forwarding path determination and programming function.

The separation of functional planes also resulted in the definition of new overlay and underlay functionality. Network overlays defined that tunnel endpoints terminated on routers and switches. The physical devices executed the protocols to handle resiliency and loops. Some examples are OTV, VXLAN, VPLS, and LISP.

Host overlays defined that tunnel endpoints terminated on virtual nodes. Examples of host overlays are VXLAN, NVGRE, and STT. Finally, integrated overlays allowed for physical or virtual endpoints in tunnel termination. The Cisco ACI fabric with Nexus 9000 series switches are examples of integrated overlays.

The Cisco Solutions

Cisco has many offerings in the SDN space, the most prominent being the Cisco ACI fabric with Nexus 9000 series switches. Software-defined access (SDA) is enabled by Cisco DNA Center on enterprise fabric-enabled devices. Software-defined wide-area networks (SD-WANs) can be seen in the acquired technologies of Viptela, resulting in the vManage solution for central cloud management, authentication, and licensing.

Network Function Virtualization (NFV) enables cloud technology to support network functions, such as the Cisco Integrated Services Virtual Router (ISRv), ASAv, and vWLC. The Cisco Managed Services Accelerator (MSX) provides automated end-to-end SD-WAN services managed from the service provider cloud.

4. Application Programming Interfaces (APIs) | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020