(This blog has been developed in association with Praveen Jain, VP, Engineering of Cisco’s Application Policy Infrastructure Controller, Juan Lage, Principal Engineer and others)

Security is top of mind in today’s data center and cloud deployments and security architectures have continued to evolve even as new threats manifest themselves in the digital world. Today’s security administrator requires a variety of “tools” to deal with the sophisticated attacks. One such tool is the ability to segment the network.

Traditionally network administrators have allocated subnets for different applications and mapped them to VLANs as a means of providing network segmentation, partitioning and isolating domains.  This classic approach was relatively easy to implement and facilitated policy definition using Access Control Lists (ACLs) between subnets at the L3 boundary, usually the first hop router or perhaps a physical firewall.

However, this approach led to the undesired mapping of IP subnets to applications. Over time, it also led to an explosion of ACLs when subnet based policies were not sufficient (for instance, by requiring ACLs that match on specific IP Addresses). This in turn made it difficult to perform garbage collection of ACL entries when applications were decommissioned, complicating the ACL management problem.

So, while the broad constructs of segmentation are still relevant, today’s application and security requirements mandate increasingly granular methods that are more secure and operationally simpler.

This has led to the evolution of what we call as “micro-segmentation”.  Broadly, the goals of micro-segmentation are as follows

• Programmatically define segments on an increasingly granular basis allowing greater flexibility (e.g. to limit lateral movement of a threat or to quarantine a compromised endpoint  in a broader system)
• Leverage programmability to automate segment and policy managent across the entire application lifecycle (instantiation through de-commissioning)
• Enhance security and scale by enabling a Zero-Trust approach for heterogeneous workloads

Micro-segmentation with Cisco’s Application Centric Infrastructure  

Cisco’s Application Centric Infrastructure (ACI) takes a very elegant approach to micro-segmentation with policy definition separating segments from the broadcast domain. It uses a new application-aware construct called End-Point Group (or EPG) that allows application designers to define the group of endpoints that belong to the EPG regardless of their IP address or the subnet they belong to.  Further, the endpoint can be a physical server, a virtual machine, a Linux container or even legacy mainframes – i.e. the type of endpoint is normalized and therefore irrelevant, thereby offering great simplicity and flexibility in their treatment.

ACI still preserves the traditional segment, now called a Bridge Domain (or BD). IP subnets can still be assigned to Bridge Domains. This approach helps preserve any existing operational models, if required, allowing for creation of Bridge Domains with a single EPG that maps to the concept of a traditional VLAN.

The ACI architecture takes these even further.  Multiple EPGs can belong to the same Bridge Domain, and EPGs can be provisioned programmatically (in fact, just like everything else within ACI) via an open API made available through Cisco’s Application Policy Infrastructure Controller (APIC). Simply put, the EPGs in the ACI architecture are “micro-segments” of a Bridge Domain.

The figure below illustrates this approach:

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