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Promise theory

Scott Hogg | July 2, 2014
Can you really trust the network to keep promises?

Cisco Application Centric Infrastructure (ACI):

Networks can benefit from improved scalability of complex policy-based configurations.  Today, networks are loose collections of distributed independent manually-configured switches and routers.  Eventual forwarding consistency is created after the manually configured routing protocols converge to a single best path.  Promise theory can provide automation, scalability, and flexibility benefits to modern network topologies.  Promise theory is now being applied to the world of Software Defined Networking (SDN).

Cisco's relatively new Application Centric Infrastructure (ACI) is a holistic architecture for centralized automation of policy-driven application profiles.  ACI's goal is to create software flexibility, configuration agility, application-driven policy, centralized visibility, and scalability on high-performance hardware platforms for data center networks.

The ACI model is essentially a declarative model based on the concept of promise theory.  The Application Network Profile abstractly describes how an application should function.  In ACI, the End Point Group (EPG) is a set of hosts or networks and ACI "Contracts" are a set of rules governing communications between EPGs.  The configuration and centralized policy management is performed on the Cisco Application Policy Infrastructure Controller (APIC).  There are many Cisco whitepapers on ACI that describe how this architecture supports the promise theory concept.  This document in particular "Principles of Application Centric Infrastructure" reviews the promise theory approach and the ACI object model.  There were also many more details of ACI revealed at this year's Cisco Live.

Cisco has also introduced the OpFlex protocol for consideration for IETF standardization as a southbound interface that the APIC or another controller, such as OpenDaylight (ODL), can use to connect to network devices.  Cisco has partnered with a host of software vendors to help create an ecosystem of cooperating companies to develop interoperable networks using OpFlex.  Cisco intends for the OpFlex protocol to exhibit the same promise theory information model as ACI.


Abraham Lincoln had something to say about promises, "We must not promise what we ought not, lest we be called on to perform what we cannot."  However, promise theory is a powerful concept in the new age of IT virtualization.  To achieve scalability and management efficiencies, we need to have configuration management systems that allow for flexibility while striving for consistency and predictability.  There are many laws of IT and promise theory will appear more and more in the coming years as our business continue to make more requirements on the underlying infrastructure.


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