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4 Challenges Lying in the Wait of SDN

By decoupling the data and control planes of traditional networks, software-defined networking promises a new generation of low-cost hardware that software development communities can coalesce around to create cost-effective, robust network services tailored to individual needs. However, mature enterprises and networking organizations must overcome several challenges to fully realize SDN's benefits.

Following are four common challenges in SDN created by the paradigm shift of software-defined services from traditional hardware-based networking:

1. Security - Because the control plane plays such a central function in an SDN architecture, security strategies must focus on protecting the controller and authenticating an application's access to the control plane.

New services can introduce security threats as programmers and network administrators may unwittingly introduce at-risk code and extend the threat network wide through a centralized or partially distributed controller. Related, SDN's virtual nature can result in the creation of countless network segments, each with its own risk and security requirements.

2. Scalability - Since the SDN architecture includes centralized or partially distributed controllers interfacing with data planes on multiple devices, the possibility exists for the controllers to become a network bottleneck. In particular, large networks with volumes of networking requests can overwhelm controllers. As networks grow, the bottleneck tightens and network performance degrades.

Scalability may be improved with a decentralized control architecture or similar solution, such as split or fully distributed control planes. But such solutions can introduce new obstacles such as convergence and countless control instances to configure and manage.

portable
SDN is a networking architecture that decouples the data and control planes of traditional networks. The primary principle behind SDN is that the control plane within a network can be based on software that efficiently and cost effectively delivers network services over a low-cost, commodity data plane, leveraging commercial off-the-shelf hardware.
3. Interoperability - For new networks, implementing SDN is fairly straightforward -- all network devices are SDN-ready. Transitioning a legacy network to SDN is another story as the legacy network is likely supporting active business and networking systems. Enterprises and most networking environments have to transition to SDN, requiring a period of interoperability with a hybrid legacy-SDN infrastructure.

SDN and legacy network nodes can operate together, with help from an appropriate protocol that supports SDN communications while providing backward compatibility with existing IP and MPLS control plane technologies -- reducing the cost, risk, and disruption of services while transitioning to SDN.

4. Performance - Performance is the greatest issue for all networks. Regardless of how robust, secure, scalable, or interoperable a network is, it's unusable if it lacks performance.

The separate control and data plan architecture can introduce latency into SDN. In large networks this can build to an unacceptable level of delay, degrading network performance. Related, controller response time and throughput can contribute to poor performance, with the combined effect causing scalability issues.

The solution for many performance issues in large and growing networks is to push more intelligence to the data plane or move to a distributed control plane architecture of some type. While this can improve SDN performance, it's moving somewhat away from the intent of SDN and replicating traditional networks built on fully distributed intelligent devices. A balance has to be sought where virtualization is maintained without degrading network performance or introducing potential single points of failure.

Cautious Excitement
SDN clearly offers many attractive advantages and benefits over existing networking solutions, including the opportunity to respond to the growing demand for personalized IT services and support the dynamic nature of modern end users. The opportunities to provision services through software and leverage commercial off-the-shelf hardware make it an attractive way to manage networking costs while being more responsive to user needs. There's a lot to be excited about with SDN.

But as with most innovations, challenges loom large. The centralized or partially distributed nature of SDN architectures requires a new look at security, scalability, and performance. Taking time to consider each challenge goes a long way toward deploying a flexible, modern architecture without losing the steadfastness and reliability of legacy networks.

Andriy Shapochka is the principal software architect at SoftServe, where he has designed and implemented innovative cloud, Web, and mobile solutions for large-scale enterprises in a variety of sectors including healthcare, insurance, and banking. Andriy is an expert in SaaS architecture and a leading voice on Agile project management in the U.S. and Europe.