Cisco ACI: AVS and Hypervisor Integration

At this point I will assume that you already read my previous posts about:
Cisco ACI Fundamentals.
Application Network Profiles, Contracts and Outside World connection.

If you did, then great. We may proceed with the "cool" stuff, such as ACI Virtual Switch and Hypervisor Integration.

AVS (Application Virtual Switch)

AVS (Application Virtual Switch) is the ACI version of Nexus 1000v or a Cisco alternative to a VMware vSphere VDS (Virtual Distributed Switch). If you are not familiar with these - these are virtual Switches, and they "live" on the Hypervisor, such as VMware ESXi (vSwitch), Hyper-V or KVM.

AVS also has VEM (Virtual Ethernet Modules) like the OVS (you may read about the OVS in my OVS introduction for Network Engineers), but instead of the VSM (Virtual Supervisor Module) it has the APIC Controller. It can be used instead of the VDS in the vSphere, or any other Compatible Hypervisor. It uses VLAN or VXLAN encapsulation, so - a pretty standard setup.

What is a key benefit of having a Virtual Switch, such as AVS, residing directly on a Hypervisor? Most of all, AVS is not just another Switch, it´s a Remote Leaf, which means - we can extend our ACI Architecture to the Hypervisor. What we get is the possibility of Micro-Segmentation, and a huge Security and Performance improvements.

AVS can operate in the following modes:

  • Non Switching mode (previously called FEX mode), which means that you extend the leaf into the Hypervisor. This way you take all the control of the Networking from the Hypervisor and to the Leaf.
  • Local Switching (LS) Mode, that enables the Inter-EPG switching within the Host. This is exactly what VDS is today.
  • Full Switching (FS) Mode, which is still not available (On the path, apparently), and it will provide a full L3 routing on the Hypervisor.

There are 2 sets of Multicast addresses, one for the AVS and also there will be a Multicast Address per EPG.

Compared to other hypervisor-based virtual switches, AVS provides cross-consistency in features, management, and control through Application Policy Infrastructure Controller (APIC), rather than through hypervisor-specific management stations. As a key component of the overall ACI framework, AVS allows for intelligent policy enforcement and optimal traffic steering for virtual applications.

Key features include:

  • A purpose-built, virtual network edge for ACI fabric architecture.
  • Integration with the ACI management and orchestration platform to automate virtual network.
  • provisioning and application services deployments.
  • High performance and throughput.
  • Integrated visibility of both physical and virtual workloads and network paths.
  • Open APIs to extend the software-based control and orchestration of the virtual network fabric.

There are 3 Standard AVS Topologies

  1. AVS host directly connected to N9K leaf switch.
  2. AVS host connected to N9K leaf switch via FEX.
  3. AVS host connected to N9K leaf switch via UCS FI.

I recommend that you focus on the official Cisco documentation for the AVS details, as things are changing quite often. Cisco ACI and Cisco AVS

VMware integration

APIC Integrates with the VMware vCenter via the APIs, so from the APIC you can create the VDS, add the VMs to a Port Group (EPG, in ACI Terms).

VMM Domain is the Virtual Machine Manager, which basically means – the Hypervisors Manager. The number of VLANs is limited to 4k, so the VMMs expands this limitation and the same VLANs can be created in each VMM Domain. You can however configure the VMs from any of the VMM domains to belong to the same EPG.

Microsoft Integration

Windows Azure Pack is an Orchestration Layer that tells the System Center (Microsoft’s Hypervisor manager that has an APIC Plugin installed) and it tells APIC what to do.

OPFlex is running between vSwitch inside the Hyper-V and the Fabric. APIC Admin doesn’t do much here, he does the Fabric Discovery and the configuration of the vPCs and the Port Profiles, and the Azure takes care of the System Center.


OPFlex is an Open Protocol designed by Cisco as an alternative to OpenFlow. It uses a Declarative resolution, which means Push + Pull API support. It is used between the APIC and the Physical Leaf, and also between the Leaf and the “Virtual Leaf”, or the AVS (Yes, the AVS can be observer as the Virtual Leaf).

The Policy Repository needs to be the APIC for now, but an OpenDaylight controller might also be able to take this role in the future. The Policy Element is the Leaf Switch. The Endpoint Registry is a database of the TEP mappings throughout the infrastructure, and it’s stored on the Spines.


  1. Hi Mateja,

    Thanks for wonderful article. Could you please explain in 2nd diagram (where leaf, hypervisor and VM in EPG shown) AVS in local switching mode EPG propagate till AVS and inter EPG communication will east-west but Arrow shows that inter epg traffic is going toward leaf switch which is north south direction. in AVS can we create interface policies and switch polices??


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