SD-WAN: Building a network of networks

The stage is now set for a significant transformation in networking due to our ever-increasing expectation to connect anywhere and at any time. The move of applications — in particular more data hungry and time sensitive applications like video and voice — to cloud environments is driving this transformation. The combination of these factors means that no single network is going to meet an organisation’s future needs.

One of the solutions gaining momentum is to build a “network of networks” — Software Defined Wide Area Networking (SD-WAN) — designed to meet the exponentially increasing demand. This solution also offers flexibility for telecommunications network services, and at a lower cost in terms of capital and operating expenditure.

Many businesses are already reliant on Wide Area Network (WAN) services to connect offices, customers and mobile devices. However, it is worth exploring the advantages of Software Defined WANs. In most circumstances, SD-WANs can bring greater efficiency, security and flexibility.

You can’t move forward standing still

In the past, networks were static and data-centric. They were built around a fixed and inflexible connection between two points; and applications were provided in a single data centre. Today, there are typically three types of WAN connectivity:

  • High cost fixed line carrier network services – high availability, guaranteed bandwidth and quality of service
  • Mid cost 3G/4G mobile network services – providing connections anywhere at anytime, with best effort delivery and non-guaranteed bandwidth
  • Low cost fixed internet based network services – with best effort delivery and non-guaranteed bandwidth

SD-WAN essentially leverages the strengths of each network and orchestrates both physical and logical connectivity paths to allow users to connect on demand, within a network of heterogeneous devices consisting of routers, switches and firewalls. The central SD-WAN controller (Diagram 1) is coordinated by an administrator to establish and automate connectivity paths between the user and device.

Diagram 1: SD-WAN links orchestrated from a centralised controller

SD-WAN links orchestrated from a centralised controller

Establishing a super-highway network

Being able to connect anywhere and anytime places increasing demands on future networks in terms of performance. But why is SD-WAN gaining so much attention as the preferred technology of choice?

  1. Lower network service costs – Optimising service costs through ‘least cost routing’ algorithms, which would only use the higher cost Multiprotocol Label Switching (MPLS) network services when absolutely necessary.
  2. Lower network operation costs – Using templates for configuration management helps reduce the associated costs of configuring and providing new services and applications in an existing operating environment. This could include hundreds if not thousands of devices across a typical network and the network administrator no longer has to configure each device individually.
  3. Improve network security – SD-WAN provides a holistic view of the entire network and its devices, producing a “single point of truth.” This allows security expert teams to better coordinate access control, and detect and respond to malicious attacks by centralising the management of all security devices via the SDN controller.
  4. Faster deployment times of services – Automating work processes can reduce implementation time from days to minutes. Within a large and heterogeneous network infrastructure consisting of multiple vendors; the ability to automate the configuration process can improves speed of deployment by streamlining network operation, administration and management (OAM) activities.
  5. Network as a service – SD-WAN enables network bandwidth to be rapidly scaled up or down in unison with the cloud and the service platform.
  6. Open interfaces – The ability to build and maintain a network consisting of devices from multiple vendors prevents organisations from being locked in to a single vendor. This allows them to build a fully open network, where the features from multiple vendors are compatible and transferrable.
  7. Less configuration problems – As the network administrator is no longer configuring hundreds or thousands of devices manually, data quality issues associated with human error are eliminated.
  8. Services rather than network focus – A service-oriented network administration team allows staff to focus on delivering services rather than managing networks. They are more able to cope with changes in the business (such as acquisition and mergers, or connecting to third party suppliers) as the SDN controller has greater flexibility. This allows users to better plan and to scale their services up or down to better match business requirements.
  9. Improved network visibility – A distinct advantage of SD-WAN is the ability to respond in real-time to network faults and issues, and to optimise devices “on the fly.” The control plane for all devices is now centrally based in the SDN controller, which allows for the management and monitoring of the end-to-end operations of the network architecture and status.

Can we expect many bumps in the road?

Software defined networking is a new paradigm that will present some challenges. So, what do you need to be mindful of when implementing SD-WAN? Are there many roadblocks and, if so, can we find ways around them?

  1. Physical security of the SD-WAN central controller – The controller is a powerful tool that grants extensive administrative access to the entire network. It should go without saying that the network needs to be secured from persons with malicious intent.
  2. Single point-of-failure of the SDN central controller – If the SDN controller is not functioning, whilst the network will continue to operate, new services cannot be added. From a risk management and analysis perspective, this may be unacceptable to some organisations. For example, the consequences of failure could be catastrophic for network infrastructures providing services to mission-critical applications (such as public safety, transport and utilities).
  3. Open source or vendor proprietary SDN Central controller – This is a choice that is complicated, and will depend heavily on the business requirements and priorities that are identified. Don’t jump in the deep-end here – do your homework and make a well-considered selection.

 Starting Your Journey

Demand for faster, better, more secure networks isn’t going away any time soon. SD-WAN allows existing and new network technologies to coexist and join together to form a “network of networks.” Clearly, the advantages far outweigh the disadvantages. And, over time, many of the current challenges facing this technology will be fixed or dissipate as vendors refine and improve the offering. SD-WAN needs to be on the agenda for all organisations as we continue the journey into the digital age.

David Lim

David Lim is a Senior ICT Consultant with more than 11 years’ experience across multiple sectors including transport, resources and telecommunications. David has successfully designed and delivered a wide range of critical communication infrastructures that are capable of supporting mission-critical operation technology and enterprise-level user applications. David has developed a keen interest and expertise in strategic planning and digital transformation of the networks to meet emerging business needs. He has provided advisory guidance and consultancy on asset investment planning to balance between risk, cost and performance.


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Protecting software-defined networks: The Open Security Controller

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  1. Good article. Hate to think that even network administrator jobs cannot escape automation and artificial intelligence.


    • Thank you for the feedback Jerry. It is very likely that some network administrator may have doubts and uncertainty regarding this change. However, as I have highlighted in the blog, automation frees up the administration team from the day-to-day running of the network and allows them to concentrate their efforts to optimise the performance of it to either reduce cost, improve service offering and/or maximize productivity.


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