At WhiteSpider, we’ve supported clients across industries in transforming their data centres with Cisco ACI. And while it offers powerful capabilities, we know it can raise just as many questions – especially when you’re getting started or migrating from a traditional network.
In this post, we’re tackling some of the most common ACI questions – and clearing up a few myths along the way.
What are common challenges or pitfalls in deploying Cisco ACI?
Let’s start with the elephant in the room – ACI isn’t a plug-and-play solution. Yes, it’s transformative, but like any major shift, it comes with challenges:
- Complexity at first glance: ACI’s concepts – tenants, EPGs, contracts – require a mindset shift from traditional networking. The initial learning curve can feel steep.
- Design is everything: A poor initial fabric or policy design can lead to pain down the road. We often help clients who need to rework their ACI implementation months after deployment.
- Ongoing policy management: With great control comes great responsibility. ACI gives you granular visibility and control, but that means someone needs to manage it properly.
🔍 WhiteSpider Insight: We recommend a design-first approach with clear objectives and expert-led workshops to flatten the learning curve and avoid rework.
How does Cisco ACI handle multi-tenancy and segmentation?
One of ACI’s biggest strengths is its ability to segment traffic cleanly and securely across tenants, apps, and users.
- Tenants are isolated virtual containers – ideal for separating business units or environments.
- VRFs keep routing domains separate within those tenants.
- Bridge domains manage Layer 2 domains and associate with EPGs.
- Contracts define how (or if) different EPGs communicate, adding a firewall-like policy layer natively into the fabric.
🚫 Myth Busted: You don’t need a separate physical network for each tenant – ACI does the heavy lifting virtually, without complexity.
How does Cisco ACI support Hybrid or Multi-Cloud environments?
As businesses extend workloads across on-prem and cloud, ACI is designed to go with you:
- ACI Anywhere provides consistent policy and control across data centres and cloud platforms.
- Multi-site architecture lets you interconnect multiple ACI fabrics, with the ability to manage and apply consistent policy from a single controller.
- Remote Leaf technology allows you to extend your fabric to smaller or edge locations without full spine/leaf infrastructure.
- Cloud ACI supports native integration with AWS and Azure – enabling policy consistency from on-prem to cloud.
🌐 Real-world benefit: With unified policy enforcement, you reduce the risk of configuration drift between environments.
What are EPGs, Contracts, Tenants, and Bridge Domains in ACI?
This is the heart of ACI’s policy-based model – and it’s what sets it apart from legacy networking:
- EPGs (Endpoint Groups) = logical groupings of devices or workloads that should be treated with similar connectivity or security requirements.
- Contracts = policy rules that allow (or deny) traffic between EPGs.
- Tenants = isolated network environments (think dev, test, prod – or even different clients).
- BDs (Bridge Domains) = a Layer-2 forwarding domain within the ACI fabric. A BD associates with an EPG and defines how endpoint traffic is forwarded through the fabric.
Think of EPGs and BDs as replacing VLANs and contracts replacing Access Control Lists (ACLs) – but with a lot more flexibility and context-awareness.
🧠 Pro Tip: You define “who can talk to whom” with business intent, not box-by-box configs.
How does ACI integrate with existing network infrastructure and security tools?
One concern we often hear: “Can I bring ACI into my current environment without breaking everything?”
The answer is yes. ACI is designed for brownfield and greenfield deployments:
- You can integrate with your existing Layer 3 networks through L3Outs.
- Firewalls, load balancers, and other security appliances can be inserted into the policy chain via service graphs.
- Migration of workloads from your existing environment into ACI can be staged – so you’re not doing a big-bang cutover.
🛠️ WhiteSpider in action: We’ve helped clients integrate ACI alongside their legacy networks, then phase in modernisation as confidence builds.
How does policy enforcement work in ACI?
ACI’s policy model is declarative – you tell the APIC what outcome you want to achieve, and the policy is automatically pushed out to the fabric.
- Security policies are enforced through applying contracts between EPGs.
- These contracts define filters, rules, and directional traffic flow.
- Policies are applied centrally via the APIC, so changes don’t require logging into individual switches.
🔒 Bonus: Since policies are abstracted from the underlying network, ACI can automatically reapply them even when workloads move – perfect for modern, redundant, and dynamic data centre environments.
Final thoughts
Cisco ACI is a key enabler for organisations reimagining their data centres to meet the demands of modern business – but it’s not without nuance. That’s why we work closely with IT leaders and managers who are transforming their infrastructure to deliver greater speed, security, and scalability.
While ACI offers extensive capabilities – from policy-driven automation to unified management – it also introduces architectural and operational complexity. Our role is to simplify that complexity, ensuring a smooth deployment and helping you realise the full benefits of Software-Defined Networking.
Hopefully this clears up some of the most frequent questions (and myths) we hear from clients on Cisco ACI.
Got more questions? Let’s talk. Whether you’re starting your ACI journey or looking to optimise an existing fabric, we’re here to help make the complex, simple.