There are a lot of network options out there, and while it’s fun to talk about them in technology terms there may be a more fundamental issue to address. Network services have always involved multiple layers, and it’s always been convenient to think of infrastructure as being either “connection” or “transport”. In the classic services of today (Ethernet and IP) and in the venerable OSI model, these two things are both in the operator domain. That might change, and we might see some (and just maybe, all) services migrate to a more user-hosted connection model. Which, in turn, could change the network service market dynamic. And all because of SD-WAN.
Networks provide information transport and connectivity, meaning that they can move bits and address endpoints. The old conceptualization of network service was simple—everything that consumed a service had an address in the service address space. It’s not that simple any more, for a variety of reasons. Nearly every Internet user employs Network Address Translation (NAT) to allow all the home devices to use the Internet without requiring they all have their own unique IP addresses. Nearly every enterprise employs virtual private networks (VPNs) or LANs (VLANs) because they don’t want their company addresses to be visible on the Internet.
An even broader and more interesting idea is also an old one, which is “tunnel networking”. If you use traditional “network services” like the Internet or Ethernet for transport, you could build tunnels using some protocol (MPLS, L2TP, PPTP…you name it) and treat these tunnels as though they were wires, my “virtual wire” concept. That means you could build a connection network on top of a network service, providing “routing” or “switching” across your tunnels just as you might once have done with real private line connections.
Nicira took this a step forward by bundling the “tunnel” protocol and the “routing” processes into a software package and calling it software-defined networking. The model is incredibly powerful in virtualization, cloud, and NFV applications because it lets you build a bunch of tenant/application networks in parallel and share the real infrastructure among them.
In a broad sense (which isn’t always how vendors present it), Software-Defined WAN (SD-WAN) arguably uses this same model but in one or more different ways. With SD-WAN the goal may be to collect sites/users onto a single “virtual network” when there is no single common physical network service available to do that. You could combine people on the Internet with those who had a private VPN or even a VLAN connection. In some cases, you might create a virtual connection by building multiple parallel tunnels (over different networks or even over the same one, but with diverse routing) and combining them.
Finally, the Metro Ethernet Forum has proposed its “Third Network” model, which not surprisingly makes Ethernet connections the physical framework of networking and builds other services by creating some form of overlay network—back to tunnels or virtual paths. Unlike the other approaches, the MEF model is an inside-out or operator-driven vision, a way of creating infrastructure that takes the most dynamic aspect of networking (connectivity) out of the hands of traditional technology.
If we leave the Internet aside for the moment, it’s easy to see that we could move all current network services to an overlay approach. The user could be given a choice of hosting their own router/switch elements (as devices, as software, as VNFs), buying internal-to-the-real-network instances from operators, or both. We could create VPNs that would look as they do today, but that didn’t require Level 3 services from operators at all.
All of this seems part of a broad trend toward the separation of function and structure. Oracle just announced a version of its public cloud software designed to be inserted into customers’ own data centers to bypass problems (real regulatory or policy problems, or just executive resistance) to moving key applications into the public cloud. This frames the notion of “public cloud” not as a business model but as a service technology layer that could then ride on whatever infrastructure technology is optimum.
This division, which corresponds to my last phase of virtual network evolution, is interesting because it could come about both through the actions of network buyers, at least for enterprise services, and through the action of the network operators. If service-layer technology is a relatively inexpensive overlay rather than an expensive collection of devices, then the operators might indeed want to promote it. If operators were to deploy virtual-wire technology in SDN or other form (including the MEF’s “third network”) then it would promote the service/infrastructure dualism.
Enterprise buyers could do this on their own, and SD-WAN concepts lead in that direction. The notion of multi-infrastructure service is at the least a path to infrastructure-independent services, and some implementations (Silver Peak, for example) are explicitly dualistic (or multiplistic) in terms of what they can run on. These bridge across infrastructures with a service, so they could be used by enterprises to create something like the MEF’s third-network vision even if the operators who are the intended target somehow don’t see the light.
Another force that could influence a move to an overlay model is the managed service provider market. We already know from NFV experience that MSPs are a growing force, largely because they address a market segment that needs networking but can’t retain (or afford) the skilled labor needed to run one on their own. In NFV, MSPs have been able to lead the market for vCPE services because their value proposition is to substitute service-less technology for that which requires internal support. The same thing could happen with overlay services.
If we look at things this way, then the SD-WAN space could be the most disruptive service technology out there. It could transform the network model, work both from the supply side and demand side, and it’s currently largely driven by startups or companies who aren’t part of the L2/L3 mainstream who have a vested interest in keeping things as they are. Since the overlay model favors SDN and fiber, it might be the perfect match for a player like ADVA, Ciena, or Infinera, and all of these companies have the technology to promote the notion. We’ll see if they do.