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What is real "open" SDN?
If you consult Merriam-Webster's dictionary for a definition of the word "open," you won't find a single clear and concise definition -- in fact, you will find 19 of them. So it's no surprise the landscape of SDN is also a bit confusing when it comes to the same concept of "open," which gets enthusiastically thrown around by vendors and standards-bearers alike. Looking at a few categories of "open" may help to demystify the landscape.
OpenFlow is an open protocol that promises solutions that are non-proprietary and should be applicable in heterogeneous environments.
NETCONF, XMPP and YANG are open standards that anyone can implement, but as with Simple Network Management Protocol (SNMP) Management Information Bases (MIBs), devices supporting these protocols will implement their own information model, which can result in proprietary solutions.
Cisco onePK is a proprietary protocol that is implemented on Cisco devices, but any customer can write SDN-type centralized applications to it.
OpenFlow-based controllers can be open source (e.g. Beacon, Floodlight, Ryu) or commercial (e.g. HP or NEC). These controllers should interoperate with any Openflow-supporting device, resulting in the possibility of a multi-vendor network environment.
Multi-protocol controllers are mostly open source, the most prominent being OpenDaylight, which allows multiple southbound protocols (e.g. Openflow, NETCONF). Using the Openflow plug-in on these controllers allows for a multi-vendor device environment. Using other protocols with proprietary information models will often yield only a single-vendor device environment.
Closed SDN solutions such as VMware provide no API for programmability, and are therefore not intended for SDN application development by customers or device vendors.
Open APIs are provided by just about every SDN or SDN-like controller or solution, including Openflow-only controllers; OpenDaylight-based controllers; proprietary open source controllers, like OpenContrail; and Cisco's various SDN systems, like onePK and APIC. Anyone can write applications to these APIs, but the proprietary versions will only work with that vendor's devices.
All of these facets of openness have their strengths and weaknesses. When your friendly neighborhood networking vendor comes calling and begins to wax eloquent on the exceptional "openness" of their product, it would be wise to understand just what type of "open" he or she is talking about before you whip out your fountain pen and sign on the dotted line.
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