SD-WAN Vs Traditional WAN | Difference between SD-WAN and Traditional WAN

This page compares SD-WAN Vs Traditional WAN and mentions difference between SD-WAN and Traditional WAN. SD-WAN stands for Software Defined WAN (Wide Area Network).

As we know traditional WAN consists of multiple single function devices which connects via different WAN links. This leads to complexity for branch IT management. Moreover it requires more number of devices to be maintained.

SD-WAN offers many benefits over traditional WAN. As a result SD-WAN has been adopted by companies already using traditional WAN.

Traditional WAN

WAN (Wide Area Networking)

• In traditional WAN, each instance of data plane contains its own control plane. This makes programming difficult.
• Moreover traditional WAN architecture is static and private. This inhibits migration to dynamic and public cloud environments.
• The traditional WAN has complexity during branch deployments as it depends on various transport mediums used such as DSL, coaxial, fiber, 4G LTE etc.
• Traditional WAN requires separate security and management requirements due to disparate traffic flows. This leads to higher complexity to manage various branch operations and consecutively increases operational cost due to skilled resource requirements.
• Figure-1 depicts block diagram of traditional WAN system along with its interface components.

Following are the challenges associated with traditional WAN solutions which are being addressed by SD-WAN.
• QoS parameters (e.g. bandwidth) are configured manually and do not adapt to changes in link conditions.
• Routing protocols are tuned manually to load balance the traffic.
• Ineffective use of all the available WAN resources. WAN circuits remains often in passive standby mode. They are used only in hard failover situations.
• When link failure occurs in traditional WAN, it requires several seconds to restore. This results into poor end user experience.
• Traditional WAN uses IPSec for authentication which requires pre-shared key to devices. It is difficult to manage sharing of key across large number of devices.

SD-WAN (Software Defined WAN)


SD-WAN separates functionality of networking devices into control plane and data plane. As we know control plane is responsible for signaling traffic and routing decisions where as data plane carriers application and user data. Unlike traditional WAN devices where each instance of data plane contains its own control plane, in SD-WAN one logical instance of control plane serves multiple instances of data plane (typically switches, routers). This separation makes programming and controlling of all the transport mediums easier. Figure-2 depicts block diagram of typical SD-WAN system along with its interface components.

SD-WAN is a technology which distributes traffic between branch offices and data center sites via most appropriate transport mediums using software defined networking SDN) concepts. Hence SD-WAN is considered to be transport-agnostic.

Following are the silent features of SD-WAN system.
• It uses centralized control plane based architecture. Control plane takes care of larger and diverse set of data plane components.
• It uses standard Open Flow Protocol. It enables the communication between control plane and various data plane components. The company by name Viptela has developed OMP protocol specifically developed for SD-WAN system. Viptela has been acquired by Cisco. OMP stands for Overlay Management Protocol. Hence protocols such as OSPF, BGP etc. are not required in SD-WAN system.
• It delivers transport independent, secure and reliable network.
• It uses standard encryption such as AES and hence delivers secure connectivity over any type of transport mediums. Some SD-WAN services also use IPsec in order to authenticate network traffic between branch offices and data center sites.
• It is easy to migrate from traditional WAN into SD-WAN using different approaches such as inline path, out of path, thin branch etc. All these approaches use BGP to interface legacy branch with SD-WAN branch.
• SD-WAN services to users include easy to use management console to manage traffic, assign policies, configure devices (switches, routers, firewalls) etc.
• SD-WAN simplifies network by automating certain tasks such as deployments, configurations and operations.
• SD-WAN improves cost effectiveness and flexibility by leveraging commercially available hardware and network devices or servers.

Following table summarizes major difference between SD-WAN and Traditional WAN.

Traditional WAN SD-WAN
Each instance of data plane contains its own control plane. Moreover there is no central controller. Hence programming and management is difficult. Each logical instance of control plane serves multiple instances of data plane. Due to centralized SD-WAN controller, programming and management is easy.
It is not transport agnostic. It is transport agnostic.
It uses overlay networks such as MPLS. It uses overlay networks such as VXLAN, IPsec, GRE, DMVPN etc.
It delivers higher performance. It delivers very high performance.
It uses traditional routing protocols such as BGP, OSPF etc. It uses flow based traffic management protocols such as OMP (Overlay Management Protocol).
It uses vertically integrated CPE model as hardware models. It uses hardware models which are deployed on X86 virtualization.
It offers expensive bandwidth based solutions. It offers low cost WAN solutions.
It uses complex infrastructure. It uses simple infrastructure.
It offers high security. It offers very high security.
It offers WAN with good reliability. It offers WAN with excellent reliability.
Automation and analytics features are not supported. Automation and analytics features are available.

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