SDN fabric controllers

Credit: sFlow.com

There is an ongoing debate in the software defined networking community about the functional split between a software edge and the physical core. Brad Hedlund argues the case in On choosing VMware NSX or Cisco ACI that a software only solution maximizes flexibility and creates fluid resource pools. Brad argues for a network overlay architecture that is entirely software based and completely independent of the underlying physical network. On the other hand, Ivan Pepelnjak argues in Overlay-to-underlay network interactions: document your hidden assumptions that the physical core cannot be ignored and, when you get past the marketing hype, even the proponents of network virtualization acknowledge the importance of the physical network in delivering edge services.

Despite differences, the advantages of a software based network edge are compelling and there is emerging consensus behind this architecture with  a large number of solutions available, including: Hadoop, Mesos, OpenStack, VMware NSX, Juniper OpenContrail, Midokura Midonet, Nuage Networks Virtual Services Platform, CPLANE Dynamic Virtual Networks and PLUMgrid Open Networking Suite.

In addition, the move to a software based network edge is leading to the adoption of configuration management and deployment tools from the DevOps community such as Puppet, Chef, Ansible, CFEngine, and Salt. As network switches become more open, these same tools are increasingly being used to manage switch configurations, reducing operational complexity and increasing agility by coordinating network, server, and application configurations.

The following articles from network virtualization proponents touch on the need for visibility and performance from the physical core:

• Demo: End to end, hop by hop, physical and virtual network flow visibility with NSX, Brad Hedlund
• A Tale of Two Layers – Correlating Overlay and Physical Network Data for better OpenStack Network Analytics, OpenContrail Blog
• Elephant Detection in the vSwitch With Performance Handling in the Underlay, Network Heresy

While acknowledging the dependency on the underlying physical fabric, the articles don't offer practical solutions to deliver comprehensive visibility and automated management of the physical network to support the needs of a software defined edge.

In this evolving environment, how does software defined networking apply to the physical core and deliver the visibility and control needed to support the emerging software edge?

Credit: Cisco ACI

Cisco's Application Centric Infrastructure (ACI) is one approach. The monolithic Application Centric Infrastructure Controller (APIC) uses Cisco's OpFlex protocol to orchestrate networking, storage, compute and application services.

The recent announcement of Switch Fabric Accelerator (SFA) offers a modular alternative to Cisco ACI. The controller leverages open APIs to monitor and control network devices, and works with existing edge controllers and configuration management tools to deliver the visibility and control of physical network resources needed to support current and emerging edge services.

The following table compares the two approaches:

	Cisco ACI	InMon SFA
Switch vendors	Cisco only - Nexus 9K	Inexpensive commodity switches from multiple vendors, including: Alcatel-Lucent Enterprise, Arista, Brocade, Cisco Nexus 3K, Cumulus, Dell, Edge-Core, Extreme, Huawei, IBM, HP, Juniper, Mellanox, NEC, Pica8, Pluribus, Quanta, ZTE
Switch hardware	Custom Application Leaf Engine (ALE) chip + merchant silicon ASIC	Merchant silicon ASICs from Broadcom, Intel or Marvell
Software vSwitch	Cisco Application Virtual Switch managed by Cisco APIC	Agnostic. Choose vSwitch to maximize functionality of edge. vSwitch is managed by edge controller.
Visibility		Analytics based on industry standard sFlow measurement
Boost throughput	Cisco proprietary ALE chip and proprietary VxLAN extension	Controls based on industry standard sFlow measurement and hybrid control API
Reduce latency	Cisco proprietary ALE chip and proprietary VxLAN extension	Controls based on DSCP/QoS, industry standard measurement and hybrid control API
Limit impact of DDoS attacks		Controls based on industry standard sFlow measurements and hybrid control API

A loosely federated approach allows customers to benefit from a number of important trends: inexpensive bare metal / white box switches, rich ecosystem of edge networking software, network function virtualization, and well established DevOps orchestration tools. On the other hand, tight integration limits choice and locks customers into Cisco's hardware and ecosystem of partners, increasing cost without delivering clear benefits.