• 09/09/2014
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Software-Defined WAN: A Primer

Enterprise WANs are costly and complex to manage. SD-WAN technology can help by automating the configuration of WAN edge routers.

In the world of software-defined networking, the focus has been on the data center. SDN in the data center has enabled integration with automated systems, allowing enterprises to build virtual networks, provide micro-segmentation, and integrate service chaining. That functionality has demonstrated SDN's value and brings networking a step closer to the automated world enjoyed by virtualization professionals for many years.

However, the data center is not the only part of IT that could use a software-defined hand. Enterprise wide area networks are sources of cost and complexity. Stitching together remote offices via a provider's MPLS network is highly functional -- with L2 or L3 connectivity options and guaranteed privacy and quality of service -- but also expensive. Broadband options lack the rich functionality of a provider's MPLS cloud, but they grant much more bandwidth for the money spent.

Learn more about the software-defined WAN at Interop New York, where Greg Ferro will discuss "How the Software-Defined WAN Changes Everything for the Better." Register now for Interop, Sept. 29 to Oct. 3 in New York City.

Ideally, an organization would be able to use broadband connectivity for most interoffice network traffic while putting only mission-critical or quality-sensitive traffic over private MPLS links. Though it's possible to configure routers to do this sort of hybrid WAN manually using technologies like Dynamic Multipoint VPN, Cisco Performance Routing (PfR), and real-time quality measurements, the resulting configuration is complex. Even with such a WAN implementation, it's unlikely that the initial deployment will be the final one. As application profiles change, WAN router configurations need to be changed to accommodate the current traffic mix.

Here's where software-defined WAN products can help. SD-WAN addresses these challenges by automating the ongoing configuration of WAN edge routers, running traffic over a hybrid of public broadband, private MPLS links, and other WAN links such as LTE. The end result should be an enterprise network edge with these three attributes:

1. Lower cost
With a software-defined WAN, an enterprise should be able to rely more on broadband and less on private links. Broadband won't provide quality guarantees, so the SD-WAN will take active measurements between endpoints to know whether the broadband link is capable of carrying, say, voice or video traffic reliably. As Skype users know, it's entirely possible to run voice and video over the public Internet.

That said, SD-WAN can handle those occasions where broadband quality is inferior and shunt traffic over the private link with guaranteed quality only as needed. As a result, organizations should be able invest in larger, cheaper broadband links and minimize the size of their expensive private links.

2. Reduced complexity
Configuring a hybrid WAN by hand is a challenge. Routing protocols, unless influenced by an outside source, choose a single best path to get between two sites and stick with it. Routing protocols don't react to changing network circumstances such as packet loss, excessive jitter, or congested links; routing protocol metrics simply don't include that sort of information in their best path calculations. Measurement techniques like IP SLA or PfR can artificially change metrics or otherwise override the normal behavior of a routing protocol, but these are tricky tools to configure.

SD-WAN handles this work for an organization in an automated way, routing and rerouting traffic dynamically based on the current state of the network. The IT team tells the SD-WAN application how certain traffic should be treated, and the solution takes care of the rest. To be more precise, the complexity doesn't actually go away -- it's simply hidden by the SD-WAN application doing all of the heavy lifting.

3. Increased flexibility
SD-WAN technology enables the hybrid WAN to react to changing network conditions automatically. That, by itself, means the WAN is flexible in a way that it likely wasn't before. But in addition to that flexibility, an organization gains back time for its IT staff, as well as budget in the form of reduced capex for new circuits and opex for the WAN infrastructure.

Software-defined WAN caveats
Perhaps the greatest challenge when evaluating SD-WAN technologies is the ROI calculation. The capex and opex of the SD-WAN solution will need to be compared to the overall cost of the WAN itself. The idea is that a hybrid WAN that makes heavier use of cheap broadband should allow for smaller private links; some offices might not require private links at all.

As a result, this ROI calculation could reveal that an SD-WAN purchase will pay for itself or even save money. The catch in downsizing or eliminating private circuits is that most carriers lock their enterprise customers in with a multi-year contract. Thus, penalties for early termination or service-level changes could further impact ROI.

Another consideration when evaluating SD-WAN technology is that of vendor lock-in. There are several SD-WAN products, and they are all different and incompatible. Some layer on to a WAN; some replace WAN hardware with their own. An evaluation process should carefully consider the long-term commitment to the vendor.

Closely tied to this is the notion that an SD-WAN solution must be integrated into an organization's WAN. If the product requires hardware replacement, has that hardware already been depreciated? This could be a hidden cost that needs to be considered, beyond the practical operational costs of implementing a new IT solution.

Next: Software-defined WAN products



Ethan, do you think many more vendors will jump into this software-defined WAN space? 

Re: market

Hello all,

@ Marcia, Good question.

Re: market

Marcia, yes, I believe so. SDN WAN is a natural evolution for SDN vendors in general. Cisco with their IWAN product mentioned in the piece is one example of this. I think other SDN vendors are going to take their data center expertise and apply it to the WAN space. There's a number of interesting problems to solve in the WAN. This initial problem (easily managing hybrid WAN) is just one. There are other problems to solve, such as extending virtual networks outside of the data center to the WAN. While this has been done with MPLS for a long time, many potential customers don't want to upgrade their infrastructure to support MPLS, or don't want to have to develop the expertise in-house to run an MPLS network. SD-WAN can fill in that gap. So, as network virtualization and microsegmentation concepts start to take hold in enterprises especially, expect the SD-WAN market to see more entrants.

Re: market is the new player in SDN WAN.

The startup from Karlsruhe, Germany offers SDN-enabled gateways, switches, and access points managed from a cloud console.

Software Defined

Hello everyone,
@ Ethan, thanks for this post. Great information!
Can  we say; all concepts, technologies ... in networking will be based on this approach, we got SDN, SDDC, SDS, now SDVPN SD-WAN, ... so SDX.
That's Good so!

@ Marcia, Sue, what do you think, have an article which explains, with solutions, clearly each actual SDx
(maybe  titled "Some basics SDx you should know" -- or  i don't know)

Software Defined Radio Access Network (SD-RAN) -- Possible ?

What i'm looking forward to see ...
Everyday, i remark how complex task is each part of the life cycle of a telecom radio access network; from the design

to the optimization (take environnements and user behaviour into count, too much parameters to tune everyday, large

deployment, add capacity, densify,...)
So, have an SD approach for the Radio Access Network (maybe SD-RAN) in order to have a kind of automation or ---- will be a great great blessing for Radio Network design & optimisation engineer  in my opinion :) . I ask myself what that will be?

Can someone tell us something?


Re: Software Defined Radio Access Network (SD-RAN) -- Possible ?

Jerome - good points, interesting problems, viable use-case in my opinion, but not a market I personally have much experience with. Who are the radio suppliers you typically work with? I can poke around and see what I can find out.

Re: Software Defined Radio Access Network (SD-RAN) -- Possible ?


@ Ethan, ok thanks! ALU, Ericsson and Huawei.

"...but not a market" you said. Could you explain, please?

The De-evolution of WAN Evolution

Good points, Ethan. When Silver Peak was developing our Unity Intelligent WAN fabric (launched in August), I had a number of internal conversations about the "de-evolution of WAN evolution."

The new WAN is exciting for our industry. It lets us radically rethink how we build our network, in part by embedding intelligence within the WAN. We have the smarts to select optimum paths; the smarts to reduce costs; the smarts to balance critical against non-critical traffic based on business priorities.

At the same time, though, many of the approaches that you name (and other you haven't named) take a step back from where enterprises need to be. They may provide the management interfaces and intelligence to establish SDN policies, but they fail to provide the control and acceleration to follow through on those policies.

And if they offer acceleration and control then they can't evolve in other ways. They lack the management intelligence for intelligent, dynamic control of cloud flows. They lock you into an architectural framework that may look good on a feature's list, but is very expensive to deploy. They require additional plug-ins and add-ons for full functionality. And they limit your agility by locking you into proprietary hardware. This last bit seemed particularly strange to us in a world where IT wants to virtualize more not less.

So it's delivering on the complete package that's so important. The SDN WAN needs to work for every application and service in a way that secure, scalable, and fast. Does Unity meet those standards? We think so, but I'm sure you'll be letting us know  :-). 

Re: The De-evolution of WAN Evolution

Sounds like I need to be in your briefing rotation. ;-)

Excellent analysis
Very good summary of the benefits of an intelligent SD-WAN.
SDWAN and WAN Orchestration

Mushroom Networks is a company that provides SDWAN and WAN Orchestration & Broadband Bonding solutions that takes the software defined WAN concept a step further. The software defined control goes beyond simple configuration and management, but can also provide the capability to create NFVs that are flow based and can include complex functions. The drag and drop nature of building graphs enables easy WAN Orchestration even for complex WAN orchestration algorithms that can achieve SLAs and QoS targets over challenging WAN setups.