Top 50 CISCO ACI interview questions & answers

Cisco ACI is a part of Software Defined Network (SDN) product portfolio from Cisco . Cisco ACI is an emerging technology on DC build up and disruptive technology for traditional networking .This Question and Answers guide will help you to understand Cisco ACI from basics to advanced level and give confidence to tackling the interviews with positive result . You can download PDF of 50 Q&A from here by contributing small amount of money for our effort.

1.What is Cisco ACI.?
Cisco ACI, the industry-leading software-defined networking solution, facilitates application agility and data center automation with two important concepts from SDN solution, overlays and centralized control. ACI is a is a well defined architecture with centralised automation and policy-driven application profiles. ACI uses a centralised controller called the Application Policy Infrastructure Controller (APIC),It is the controller that creates application policies for the data center infrastructure.

2. What are the three components of ACI architecture .?
Application Network Profile (ANP)– a collection of end-point groups (EPG), their connections, and the policies that define those connections
Application Policy Infrastructure Controller (APIC)– a centralized software controller that manages downstream switches and act as management plane.
ACI fabric : This is connection of Spine and Leaf switches. In the ACI world Spine and Leaf are the Cisco Nexus 9000 Series Switches (N9k) , and they are act as Control and the Data plane of the ACI. It is running re written version of NX-OS in ACI mode.

3. Describe about ACI Fabric connection terminology.?
• You should use One or more spine switches to be connected to each Leaf, Models supported are Cisco Nexus 9336PQ, 9504, 9508, or 9516 switches
• You should use One or more leaf switches to be connected to End Points and APIC cluster , Models supported are Cisco Nexus 93128TX, 9332PQ, 9372PX, 9372PX-E, 9372TX, 9396PX, or 9396TX etc switches
• Spin switches can be connected to leaf switches but not each other.
• Leaf switches can be connected only to spine switches and endpoint devices including APIC devices , so this means APIC will be connected only to Leaf switches
• ACI Switches are not running spanning tree.
• Minimum 3 APIC controller should require in ACI fabric
• Max APIC can be used are 5
• Max Spine switches can be used are 6
• Max Leaf switches can be used are 200

4. What is the use of Application Policy Infrastructure Controller (APIC) on ACI Fabric.?
This is the network controller is responsible for provisioning policies to physical and virtual devices that belong to an ACI fabric. Minimum a cluster of three controllers is used. Following are the main APIC features.

  • Application and topology monitoring and troubleshooting
  • APIC shows Physical and logical topology (who is connected to whome)
  • Third-party integration (Layer 4 through Layer 7 [L4-L7] services & VMware vCenter/ vShield)
  • Image management (spine and leaf)
  • Cisco ACI inventory and configuration
  • Implementation on a distributed framework across a cluster of appliances
  • Health scores for critical managed objects (tenants, application profiles, switches, etc.)
  • Fault, event, and performance management
  • Cisco Application Virtual Switch (AVS), which can be used as a virtual leaf switch

5. How Cisco ACI differs from other SDN controllers.?
Open SDN architecture separates control plane and data plane . Control plane resides on the central controller and data plane resides on switches. If the switches lost connection to controller, it won’t function for new connections and applying traffic policies. In CIsco ACI architecture , the APIC is not control plane, rather switches still hold control plane and data plane and can function properly if the controller down.

6. What are the different object model implementation in ACI.?
Within the ACI object model, there are essentially three stages of implementation of the model, the Logical Model, the Resolved Model, and the Concrete Model.
Logical Model: The logical model is the interface for the system. Administrators are interacting with the logical model through the API, CLI, or GUI. This is a Policy layer which include endpoint configuration on the controller .Changes to the logical model are then pushed down to the concrete model, which becomes the hardware and software configuration.
Resolved Model : The Resolved Model is the abstract model expression that the APIC resolves from the logical model. This is essentially the elemental configuration components that would be delivered to the physical infrastructure when the policy must be executed (such as when an endpoint connects to a leaf)
Concrete Model : The Concrete Model is the actual in-state configuration delivered to each individual fabric member based on the resolved model and the Endpoints attached to the fabric.This is include actual configuration of device and resides on fabric (spines and leafes )

7.What is Policy layer and Concrete Layer in ACI model.?
Concrete layer is the ACI fabric and policy layer is controllers

8.What you mean by Tenant .?
Basically a Tenant (fvTenant) is logical container for application policies to isolate switching and routing function. A tenant represents a unit of isolation from a policy perspective, but it does not represent a private network. Tenants can represent a customer in a service provider setting, an organisation or domain in an enterprise setting, or just a convenient grouping of policies.
Four types of Tenant available

  1. User
  2. Common
  3. Management
  4. Infra

9 . Difference between management tenant and infrastructure tenant.?
Management Tenant : Used for infrastructure discovery and also used for all communication/integration with virtual machine controllers. It has separate Out Of Band (OOB) address space for APIC to Fabric communication, it is using to connect all fabric management interfaces
Infrastructure Tenant : It governs operation of fabric resources like allocating VXLAN overlays and allows fabric administrator to deploy selective shared services to tenants

10.What you mean by Context/VRF on ACI .?
The top level network construct within an ACI tenant is the VRF or Context . It is called as tenant network and available as ‘private network’ in the ACI GUI .Following are the important point about VRF’s
• A VRF defines Layer 3 address domain
• One or more bridge domain can associated with VRF
• All of the endpoints within the Layer 3 domain (VRF) must have unique IP addresses because it is possible to forward packets directly between these devices if the policy allows it.
• A tenant can contain multiple VRFs How ARP handled by ACI.?

Below are some of the additional questions available on PDF

  • How ARP and broadcast handled by ACI.?
  • Why and when you require contract in ACI Fabric.?
  • How to perform unicast routing on ACI.?
  • In Fabric, which switch will act as default gateway for pertucler subnet.?
  • How Cisco ACI differentiate Layer 2 traffic and Layer 3 traffic.?
  • How VLAN working in Cisco ACI.?
  • How can you configure trunk and access port on ACI.?
  • What is micro segmentation and how to configure.?
  • How to configure inter-VRF and Inter-tenant communication.?
  • How can you integrate Cisco ACI with VmWare.?
  • Explain about ACI fabric discovery process .?
  • Explain about traffic flow lookup on ACI fabric.?

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