Cisco ACI Architecture – Simplified (2024)

SDN Overview

Software defined networking can be defined as a new approach to design, implement and manage networks that is based on the concept of separating the network control plane and data plane, where the control plane provides an abstracted centralized view of the network.

The control plane you can think of as the brain of the network where the all the intelligence happens such as routing function ( path peering, path selection etc.)
Control plane on the other hand, you think of it as the muscular part where all the heavyload of the traffic forwarding happens.

With the classical networking approach, both of these functions as co-exist on the same network device.

Usingthe SDN approach, as highlighted earlier these two functions are separated, in whichthe control plane is Centralized and the forwarding plane is ket distributed.

As a result, SDN provide the ability of administering traffic and deploying services centrally to address changing business needs, without having to touch each individual switch or router in the forwarding plane.

OpenFlow can be considered as the first (SDN) standard that is managed by Open Networking Foundation (ONF) which facilitates the communications interface defined between the controls and forwarding layers of SDN architecture. Moreover, SDN facilitates innovations and enable efficient services automation by providing open, application programmatic interfaces (APIs).

Why SDN

According to ONF, the main key benefits of OpenFlow based SDN:

OpenFlow-based SDN creates flexibility in how the network is used, operated, and sold.
It promotes rapid service introduction through customization,
It lowers operating expenses and results in fewer errors and less network downtime because it enables automated configuration of the network and reduces manual configuration.
OpenFlow-based SDN enables virtualization of the network, and therefore the integration of the network with computing and storage.
As a standard way of conveying flow-table information to the network devices, it fosters open, multi-vendor markets.

However, OpenFlow based SDN lack to scalability, visibility, security and associated with complexity and disjoint overlays. Cisco introduced a new approach and architecture that is driven from SDN with more emphasis on the most important part in the Data center which is the application, called Application Centric infrastructure ACI .

This article will discuss Cisco ACI approach and architecture.

What is Cisco Application Centric Infrastructure

Application Centric Infrastructure (ACI) in the data center is a holistic architecture with centralized automation and policy-driven application profiles. ACI delivers software flexibility with the scalability of hardware performance that provides a robust transport network for today’s dynamic workloads. ACI is built on a network fabric that combines time-tested protocols with new innovations to create a highly flexible, scalable, and resilient architecture of low-latency, high-bandwidth links

Key characteristics of ACI include:

Simplified automation by an application-driven policy model
Application Velocity. Any Workload. Anywhere.
Centralized visibility with real-time, application health monitoring
Open software flexibility for DevOps teams and ecosystem partner integration
Investment protection by integrating with the existing fabric infrastructure e.g. Nexus 7000
Scalable performance and multi-tenancy in hardware

ACI architecture Elements

Cisco ACI architecture is a combination of high performance Hardware and software innovation and intelligence integrated with two important concepts from SDN solutions; overlays and centralized control. However the ACI utilize different approach and offer capabilities that goes beyond the typical SDN offering or what is known as Openflow based-SDN

Cisco ACI Solution architecture consists of:

A centralized policy management and Cisco Application Policy Infrastructure Controller (APIC)
The new Cisco ACI high performance Fabric Hardware
A Cisco Application Virtual Switch (AVS) for the virtual network edge
Software and hardware innovations
Integrated physical and virtual infrastructure
An open ecosystem of network, storage, management, and orchestration vendors

Cisco Application Policy Infrastructure Controller (APIC)

The Cisco ACI fabric is designed as an application-centric intelligent network. The Cisco APIC policy model is defined from the top down as a policy enforcement engine focused on the application itself and abstracting the networking functionality underneath.