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What Today’s SDN Is Not Doing for Distributed Enterprises
The SDN industry is still evolving, but when considering virtual networking solutions, think beyond the data center

Today's software-defined networking (SDN) and virtualized networking solutions focus on virtualizing network functionality within the data center and the metropolitan area network (MAN). But for typical enterprises, and those managed and cloud service providers that cater to them, these solutions are not optimized for local area network (LAN) and wide area network (WAN) edge environments within today's highly distributed infrastructures.

Where the Problem Resides
A highly distributed enterprise, such as the 50-site company depicted in the figure below, is composed of multiple inter-connected sites. The user count and device capacity at any of these sites can vary by several orders of magnitude across the enterprise. An edge router connects its site to other sites through off-site WAN services (e.g., dedicated internet or MPLS), typically provided by a separate service provider. The enterprise office (campus, branch) sites contain a preponderance of corporate end users and end devices requiring access to each other and to internet, intranet and extranet resources.

A 50-Site Distributed Enterprise Network

Each site's LAN provides access connectivity to a site's users and devices. The LAN, while a shared resource, is normally implemented through highly available, high-bandwidth layer 2 and layer 3 switches and wireless access points. Bandwidth into and out of the WAN edge is normally much more expensive and, therefore, constrained, requiring resource sharing and prioritization of the services delivered over the edge router. Each of the edge routers depicted in the diagram above is normally managed as an autonomous device, meaning that any other edge router has no awareness of the configuration of service state of every other router.

Today's legacy, hardware-based SDN approach for the distributed enterprises does not address the following requirements:

  • Reduced and predictable maintenance/support costs through centralized network management and automated lifecycle network management processes (hands-free installation, simple GUI, no CLI, no truck rolls)
  • Flexible logical addressing for both local subnetting, routing and locally hosted public servers using integrated DHCP, NAT and port forwarding services
  • Diverse, off-net access per site through multiple routing interfaces to the site's local internet/intranet/extranet connections
  • Inter-site quality of service (QoS) and security/privacy using DSCP marking, priority queuing, rate limiting, secure inter-site tunnels and site-specific VLAN flexibility
  • Secure access to local networks by client and server devices such as printers, laptops, local servers and BYOD via network access control (NAC) and authentication, authorization and accounting (AAA)

The problems that arise from not meeting these requirements boil down to higher costs and a lack of flexibility, agility and control required in today's dynamic distributed networking environments, including:

  • Greater capital expenses in acquiring high-end network devices
  • Higher and unpredictable lifecycle cost to deploy, install, provision and operate these individual, autonomous network devices due to the high labor expense involved in separately administering each edge router
  • Legacy single-purpose networking hardware not supporting any application other than network functions
  • Lengthy vendor hardware development cycles promote vendor lock-in and stifle agile software innovation

Comparative: Legacy Routed Network versus Distributed SDN
The figure below depicts a 50-site SDN deployment and provides a comparison of the Capex and Opex costs between a legacy routed network and an SDN that is optimized for distributed environments. First, the most cost-effective SDN solutions remove the dependency on expensive, special-purpose router hardware. This would mean that all networking functions, including routing, L2/L3 switching, firewall and tunnels, are completely virtualized, allowing them to be hosted on commodity x86 hypervisor-enabled servers at each site. The added benefit to this approach is that the same servers may be used to host other virtualized applications. This approach helps to reduce the upfront hardware Capex by 3:1 and the average power and cooling Opex by 5:1.

Significant Cost Savings from Distributed SDN

The virtual components in this approach are distributed among the various sites. A single virtual controller, with closely coupled virtual routing, firewall and tunneling functions, is hosted on a commodity server at a head-end facility. The data plane component, a virtual switch, is hosted on an inexpensive server at each site, inheriting layer 2/3 forwarding, routing, firewall, and tunneling functions from its parent virtual controller. A web-based lifecycle management application, running on a standard server in the enterprise headquarters, can provide authenticated access through a browser. To simplify management, it is best to have the management UI administer all workflows through an intuitive web-based GUI, rather a command-line interface (CLI).

This distributed SDN scenario realized an Opex savings of 10:1 in installation and provisioning costs and a 4:1 reduction in operations policy and management costs. Over 3 years, the average TCO savings in this environment was 4:1. These savings are realized through multiple efficiencies. All administration can be done through the GUI across the distributed enterprise, and not a CLI, with no need for on-site staff at each branch or more expensive expert support staff at the enterprise headquarters. In addition, more flexible SDN solutions can allow you to use either secure MPLS networks or less expensive end-to-end security with fully-meshed IPsec tunnels between sites.

SDN solutions that provide interoperability with legacy router components through routing protocols (e.g., OSPF/BGP/static/default) are important because they allow you to plan an at-your-pace, site-to-site infrastructure migration schedule. Also, SDN solutions to support this type of environment should have a full range of these automated features: policy-based end-to-end QoS, priority queuing, rate limiting, edge routing, and LAN features (including network address translation, port forwarding, and network access control).

Benefits to MSPs and CSPs Who Serve Enterprise Networks
MSPs and CSPs serving the managed networking needs of enterprise customers can exploit the same distributed SDN advantages through more efficient managed networking practices. These service providers can host virtual components in their own data center, terminating internet service in the data center and thereby more closely coupling managed internet service with the MSP/CSP's hosted cloud services. There's a consequent opportunity for more immediate integration of service provider data center-based services (e.g., secure hosted DNS services, SP-based SaaS service, private/public/hybrid cloud hosting services), plus there are parallel opportunities to increase service margins and average revenue per user/subscriber by replacing existing edge services with an underlying technology that is much less expensive to purchase and operate.

Summary
The immediate benefits of a distributed SDN over a legacy routed network are substantial and compelling. In this scenario, they included a Capex savings of 3:1 and an average Opex savings of 5:1. The long-term benefits of the distributed SDN approach are equally compelling with a three-year TCO averaging a 4:1 savings over legacy edge network solutions. Longer-term benefits can also include network deployment agility, enhanced network service visibility and automated, policy-controlled network recovery on service degradation.

The SDN industry is still evolving, but when considering virtual networking solutions, think beyond the data center - weigh both the short- and long-term costs and benefits behind deploying SDN in a real-world distributed enterprise environment.

About Dave Corley
Dave Corley is the Director of Product Management at Netsocket, provider of virtualized, software-defined networking.

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