Home > Routing > Nexus 9K –ACI Mode – PART 1

Nexus 9K –ACI Mode – PART 1


SDN is the Buzzword for Network Guys, How is it related to Nexus 9k in API mode.

Let’s Start with SDN to understand the co–relation between SDN and Nexus 9K (ACI Mode).

To understand SDN in network terms, SDN does decoupling of control plane and data Plane, thus decision making now done at centralized control plane with the help of software. This SDN technology can be termed as classical SDN.

Nexus 9K(SDN Implementation ) behaves in different way than classical SDN,  no decoupling of control and Data plane is done, but a policy agent is added  over control and data plane.

APIC (Application Policy Infrastructure Controllers) interact with Policy agent on Nexus 9K to push the required policy. Thus ACI can be said to be based of two component:

  1. Nexus 9k which forms the physical infrastructure
  2. APIC which takes care and control all aspects of fabric configuration.


APIC is neither the control plane nor data plane but the policy controller which holds the defined policy and can instantiate required policy.




Interesting part of the NEXUS 9K (ACI Mode) is that you cannot run config t on the device , the only method to config the nexus 9K is via APIC or GUI.

ACI used leaf and spine topology, where each leaf is connected to spine node in fabric and there is no direct connectivity between leaf to leaf or spine to spine. The model is well known as CLOS Model.



MCP (Mis Cabling Protocol) runs to avoid any interconnected between leaf. The leaf node goes to suspend in case leaf are connected to each other directly by mistake.

Traffic with the source and destination on the same leaf is treated locally, whereas all other traffic passes from ingress to egress leaf via spine switch.

All external connectivity i.e host, server, VM, router, switches etc is via leaf nodes only.

The APIC REST API is a programmatic interface to the APIC that uses REST architecture. The API accepts and returns HTTP or HTTPS messages that contain JSON or XML documents.  In other words all ACI fabric functionality is defined by the Northbound REST API and the message pushed is in form of XML or JSON.

There are different new terms involved in ACI such as Tenant, End point, Contract, application profile, switch profile, interface profile ,VXLAN ,etc  which  will be discussed in coming posts.

Smiles 🙂

Categories: Routing
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  1. 31 May 2017 at 3:38 am

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