SDN at the Edge

One of the key questions that arises when service providers consider implementing SDN is, "Will it scale?"
For service providers, they want all of the same things that the enterprises do, with the ability to monetize services, and without any additional burden on their existing IT operations, staff, and budgets.

To do this, customers should consider three areas of SDN to make their decisions: controllers, overlays, and the ability to scale.


In any SDN-driven implementation, the controller plays the role as the "brains." It is responsible for the policies, and communicating with the network infrastructure to implement those policies. It also has the programmatic interfaces that allow the operators to customize and provision the applications to manipulate the network.

There are different SDN controllers with different communication protocols on the market today. OpenDaylight, HP VAN, Ryu, ONOS, OpenFlow, VMware NSX, and Midokura MidoNet are just a handful of examples.The network infrastructure needs to be flexible and programmatic to support as many of these approaches as possible.


An overlay is a logical network that enables you to create paths and connections on top of (and in many cases, regardless of) the physical connections between the end points. More importantly, overlays are a critical construct because they enable network operators to create more virtual subnets. Subnets, in turn, support multi-tenancy connections; the overlays are virtual pipes, delivering not just bits but the ability to have virtual machines and workloads move between locations.

One overlay approach is VXLAN. A big reason for this is the laundry list of vendors that have backed it - Cisco, Arista, Broadcom, and of course, VMware (based on the capabilities of their NSX controller) just to name a few. One of the reasons VXLAN was introduced was to address the problem of limited logical scale and to create Layer 2 adjacencies across different IP networks. It all sounds great - particularly if you have infrastructure that understands VXLAN and can behave as a VXLAN Tunnel End Point (VTEP).The other key overlay approach is MPLS via Labeled BGP. VXLAN is an option for providers, but the downside is that it's a relatively new protocol. It might require new equipment to support VTEP functionality, and it will definitely require education and training on how to build networks with VXLAN.Labeled BGP is a perfectly viable solution. Service providers have extensive experience and tools to solve these problems across the WAN. They can use MPLS to establish tunnels within and between datacenters, and use Labeled BGP as the signaling mechanism to exchange the MPLS labels between BGP peers.

Providers building MPLS tunnels with protocols like Labeled BGP can use this protocol as a familiar tool set to deploy new and differentiated services for their clients.  Regardless of the approach, the network infrastructure should have a support a wide range of overlay protocols and techniques to maximize flexibility.

Scaling SDN

One of the key questions that arises when service providers consider implementing SDN is, "Will it scale?" If we examine OpenFlow as an example, old-line switch vendors will warn that OpenFlow only supports up to 2,000 flows on the Broadcom Trident II chipset, which is the most widely-used chip in network switches today. Clearly, 2,000 flows are not enough to scale a network.

SDN vendors like Pica8 have overcome this limitation by making the Ternary Content Addressable Memory (TCAM) much more efficient, and by combining the TCAM with the Forwarding Information Base (FIB). This architecture supports over 200,000 flows - enough to scale any network.


Service providers need to compete for customers, and those that can offer differentiated services quickly are going to win the race. SDN is critical for service agility and the ability to monetize services, and white box networking delivers the hardware/software disaggregation while lowering CAPEX. By using a switching OS and an array of white box switching hardware options, service providers can deploy infrastructure at the service edges of their networks that will drive rapid rollouts of differentiated services and higher revenues.


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