What is an advantage of software-defined networks as compared to traditional networks?

Software-Defined Networking (SDN) centralizes the network's control plane logic. A primary concern with this centralization is creating a single point of failure. To counteract this, production-grade SDN controllers are designed as physically distributed systems, or clusters. This distributed architecture for the control and management planes ensures high availability and resilience. If one controller node fails, another can take over seamlessly, which is a significant advantage for maintaining network stability and manageability compared to having a single, non-redundant controller or certain failure modes in traditional networks.

A. The term "concrete copy" is inaccurate. SDN controllers create and maintain an abstracted model of the network, which is what simplifies programmatic control and operations.
B. This is the opposite of how SDN functions. The core principle of SDN is the decoupling (separation) of the control plane from the data plane.
C. This is not a universal advantage. While SDN promotes the use of commodity hardware, it often requires specific capabilities (e.g., OpenFlow support) that older hardware may lack.

1. Correct Answer & Explanation Support:

Kreutz

D.

Ramos

F. M. V.

Veríssimo

P. E.

Rothenberg

C. E.

Azodolmolky

S.

& Uhlig

S. (2015). Software-Defined Networking: A Comprehensive Survey. Proceedings of the IEEE

103(1)

14–76. https://doi.org/10.1109/JPROC.2014.2371999.

In Section IV-C

"Reliability

" the paper states

"A logically centralized but physically distributed controller... can be used to improve reliability

scalability

and performance." This supports the concept of a distributed architecture providing resilience.

2. Why A is Incorrect:

Nunes

B. A. A.

Mendonca

M.

Nguyen

X. N.

Obraczka

K.

& Turletti

T. (2014). A Survey of Software-Defined Networking: Past

Present

and Future of Programmable Networks. IEEE Communications Surveys & Tutorials

16(4)

1617–1634. https://doi.org/10.1109/COMST.2014.2332453.

Section III-A

"Network OS

" explains that the controller provides "an abstract view of the network." This confirms that SDN uses abstraction

not a "concrete copy."

3. Why B is Incorrect:

Open Networking Foundation. (2012). Software-Defined Networking: The New Norm for Networks (White Paper).

On page 2

the document defines SDN with the first key attribute being: "Decoupling of the control and data planes. The control plane is removed from network devices and is implemented in a separate entity." This directly contradicts option B.

4. Why C is Incorrect:

Cisco. (2021). Cisco SD-Access Solution Design Guide (CVD).

The guide's sections on "Fabric Roles" and "Physical Layer Design" detail specific hardware requirements (e.g.

Cisco Catalyst 9000 series switches) for the underlay

demonstrating that specific

often modern

hardware is necessary for full-featured SDN implementations

contradicting the idea of simply repurposing any older hardware.