Cisco Application Centric
includes Cisco Nexus 9000 Series switches with the
Application Policy Infrastructure Controller
to run in the leaf/spine ACI fabric mode. These switches form a “fat-tree”
network by connecting each leaf node to each spine node; all other devices
connect to the leaf nodes. The
manages the ACI fabric. The recommended minimum configuration for the
is a cluster of three replicated hosts. The
fabric management functions do not operate in the data path of the fabric. The
following figure shows an overview of the leaf/spin ACI fabric.
Figure 1. ACI Fabric
The ACI fabric
provides consistent low-latency forwarding across high-bandwidth links (40
Gbps, with a 100-Gbps future capability). Traffic with the source and
destination on the same leaf switch is handled locally, and all other traffic
travels from the ingress leaf to the egress leaf through a spine switch.
Although this architecture appears as two hops from a physical perspective, it
is actually a single Layer 3 hop because the fabric operates as a single Layer
The ACI fabric
object-oriented operating system (OS) runs on each Cisco Nexus 9000 Series
node. It enables programming of objects for each configurable element of the
The ACI fabric OS
renders policies from the
into a concrete model that runs in the physical infrastructure. The concrete
model is analogous to compiled software; it is the form of the model that the
switch operating system can execute. The figure below shows the relationship of
the logical model to the concrete model and the switch OS.
Figure 2. Logical Model
Rendered into a Concrete Model
All the switch nodes contain a complete copy of the concrete model.
When an administrator creates a policy in the
that represents a configuration, the
updates the logical model. The
then performs the intermediate step of creating a fully elaborated policy that
it pushes into all the switch nodes where the concrete model is updated.
The Cisco Nexus
9000 Series switches can only execute the concrete model. Each switch has a
copy of the concrete model. If the
goes off line, the fabric keeps functioning but modifications to the fabric
policies are not possible.
is responsible for fabric activation, switch firmware management, network
policy configuration, and instantiation. While the
acts as the centralized policy and network management engine for the fabric, it
is completely removed from the data path, including the forwarding topology.
Therefore, the fabric can still forward traffic even when communication with
The Cisco Nexus 9000
Series switches offer modular and fixed 1-, 10-, and 40-Gigabit Ethernet switch
configurations that operate in either Cisco NX-OS stand-alone mode for
compatibility and consistency with the current Cisco Nexus switches or in ACI
mode to take full advantage of the
application policy-driven services and infrastructure automation features.