Overlay Networks: Is SDN-Lite Good Enough for Now?

Building an entire new SDN-optimized infrastructure is a daunting task. Perhaps the overlay approach on legacy networks isn't so bad.

By Arthur Cole | Posted Mar 21, 2014
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It’s been said, by myself and others, that the most direct way to a software defined network (SDN) is to purpose-build one from scratch. Even with the benefit of modular infrastructure, however, this is easier said than done. Fact is, the typical enterprise does not have the resources to simply remake their entire network architecture.

That means many organizations will have to make do with laying SDN atop legacy networks, imperfect as they may be, most likely using one of the various overlay techniques currently making the rounds. The general consensus seems to be that overlay technology will work reasonably well on legacy infrastructure, but they become more flexible and resilient when supported by new white box infrastructure or specialty hardware from platform providers like Cisco and Juniper.

Of course, this leads to the question: how much network flexibility do businesses really need to accomplish business objectives?

According to tech analyst Kurt Marko, many users are starting to wonder if full-blown SDN is a worthy goal after all. His work with the Open Network User Group (ONUG) centers largely on overlay networks and other priorities like integrated Layer 4-7 services and software-defined wide area technology, none of which fall under the purview of the legions of OpenFlow-based controllers currently rolling off the assembly line. Perhaps in time, OpenFlow will gain the necessary support for a wide range of networking applications, but at the moment, most vendors are only on board with the earliest version of the protocol (1.0), and there still isn’t a standard OF software control platform.

For companies like Cisco, this represents both danger and opportunity. The danger is that if the enterprise community starts to think that conversion to a full SDN platform like Cisco One or the Application Centric Infrastructure (ACI) is overkill, hardware sales are likely to take a tumble. But if overlay technology is just enough to whet the appetite for advanced network abstraction, the company is in a pretty good position when it comes to tightly integrating SDN with underlying hardware to deliver on features like greater visibility and improved management and control capabilities.

HP, too, has a lot at stake in the success of network overlay technology. The company utilizes the VXLAN format to transition current VLAN deployments into full Network Virtualization Overlays (NVOs). These can be used to create logical networks that extend way beyond the 4,000 or so IDs available on the typical VLAN. And by way beyond, we’re talking multiple millions. At the same time, the company says it can abstract network extensibility off of physical hardware, making it easier to build and maintain network topologies that stretch across broad geographic areas.

Overlays can be used for more than just SDN, though. In fact, some designers are promising network versatility without SDN at all. Cumulus Networks, for example, recently teamed up with Midokura to devise a new server design that enables line-speed application connectivity between physical and virtual servers. The system uses the Cumulus Linux OS build and the MidoNet overlay system to run traffic through a VXLAN Tunnel Endpoint (VTEP) gateway. In this way, organizations will be able to utilize web-scale infrastructure for legacy database software and other applications that don’t lend themselves to virtual environments.

These and other issues are reasons why a good network architect is such a valuable asset in the data center. A simple overlay network may not provide all the bells and whistles that a soup-to-nuts SDN platform offers, but it may suffice for the time being for organizations that have clearly defined goals in mind. At the same time, the normal refresh cycle can be reworked to incorporate longer-term goals like cloud-scale dynamic networking and application-based network configuration.

In that regard, SDN is more of a strategy than a specific technology or networking protocol. When it comes to building solutions, abstract network architectures will prove extremely flexible, but that doesn’t mean everyone has to deploy them using the same, or even similar, platforms.

Photo courtesy of Shutterstock.

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