First, there was Cisco StackWise® Virtual, providing the ability to virtualize two connected switches into a single virtual switch. Now there’s the next generation of technology, developed by Cisco IOS XE engineers, with an array of new benefits. The biggest benefit is that this virtualization technology can now run over optical fiber, so switches can be physically located up to thousands of miles away from each other.

What are Cisco StackWise Virtual and Cisco Next Generation StackWise Virtual? What other benefits does it provide? And why is physically stacking switches and hassling with complex cabling so passé?

Read on.

Increasing Operational Efficiency

Physical switch stacking solutions use proprietary cables that are laid out in complex configurations and are limited by the length of the cables. Virtualization eliminated the need to physically stack switches on top of each other. Now, using fiber, switches can be located far from each other.

Cisco StackWise Virtual is a network system virtualization technology that pairs two directly connected switches into one virtual switch. To users, the switches look like two separate physical ones. To administrators, they look like one virtual switch with the same configuration and forwarding state.

Switches in a Cisco StackWise Virtual solution increase operational efficiency by using a single control and management plane. Convergence for multicast and failover is much faster. System bandwidth can be scaled with a distributed forwarding plane. And with StackWise Virtual, pioneered by Cisco, administrators can reduce the number of software versions they have to manage by half.

How StackWise Virtual Works

The StackWise solution is an enhancement of Cisco Virtual Switching System (VSS), available on Cisco Catalyst 6500 Series switches. Cisco StackWise Virtual is an inter-chassis system link between two switches that actively forwards traffic (Figure 1) in the StackWise Virtual domain. It enables stack fabric communication over network ports to virtualize the system. The StackWise Virtual connections do not run any network protocol and remain transparent in Layer 2 and Layer 3 network topologies. The active and standby switches support local forwarding that individually performs desired lookups and forwards traffic on local links to uplink neighbors.

Cisco StackWise Virtual Link domain
Figure 1. Cisco StackWise Virtual Link domain

The ability to cluster two switch chassis together into a single, logical entity provides benefits such as higher availability and scalability and simpler management and maintenance. Cisco StackWise Virtual Link enables a loop-free Layer 2 network topology of Stackwise virtual member switches for both access and core.  The Cisco solution simplifies the Layer 3 network topology by presenting itself as one logical switch, reducing the number of routing peers in the network. The Cisco NSF feature also handles the failure scenarios optimally with the StackWise Virtual SSO so that forwarding is nonstop, even if control plane failover happens.

With solutions at both Layer 2 and Layer 3, Cisco StackWise Virtual provides faster redundancy and failover than other solutions available to enterprises.

Evolution from Data Center Solutions 

In the data center, networking vendors have used solutions like multi-chassis link aggregation groups (MC-LAG) to virtualize and aggregate multiple network connections. MC-LAG allows ports to terminate on separate chassis to provide redundancy in the event of a link failover. However, implementations of MC-LAG could be associated with other proprietary implementations and therefore implementation can vary from vendor to vendor. And at Layer 3, recomputing occurs, so convergence in the event of a failure is slowed.

Our competitors are pushing the use of the MC-LAG protocol for switch virtualization and stacking in enterprises. But on enterprise campuses, multicast and convergence requirements are much faster and more mission-critical. If a link or switch goes down, it needs to failover seamlessly and quickly to a different node.

By virtualizing at only Layer 2 to combine the stacked switch brains, Cisco StackWise Virtual provides far superior convergence performance than solutions like MC-LAG or Virtual Router Redundancy Protocol (VRRP), which require failure handling and recomputing at Layer 3.

Also, with the data plane of one node active and the other on standby, VRRP provides lower capacity (fewer data processed) compared to Cisco StackWise Virtual, which maintains an active/active data plane to provide high capacity. With both data planes always active, Cisco StackWise Virtual doubles capacity in the stacking solution, enabling more enterprise access-layer devices (e.g., access points, laptops, phones, sensors) to be supported.

StackWise Virtual Link’s single control plane also helps in failure handling because to the network the stacked switches present as a single entity. If one node fails, another node takes over. The rest of the network is undisturbed.

The Next Generation of StackWise 

Recommended for aggregation layers, collapsed aggregation, and core layers for best results, Cisco StackWise Virtual Link can be used over 40G or 100G links to ensure that the distribution of the aggregation switches can be deployed over a long distance. The next generation of the feature in Cisco IOS XE software can run on generic optical fiber, so switches can be located in adjacent buildings or on opposite ends of a continent. This gives businesses that are becoming overwhelmed with multiple physical switches in office buildings plugging into the same port much greater flexibility in switch deployment.

Now switches serving an office building with hundreds of users accessing Wi-Fi, for example, can be placed outside of the building, freeing up space and adding flexibility as requirements and office configurations change. The new version of StackWise Virtual also offers standards-based node discovery technology, enabling the automatic discovery of all nodes on the network. The future release of the Next-Generation StackWise Virtual could eliminate the restriction of a directly connected network and could connect its member nodes over Layer 2 and Layer 3.

The Next Generation StackWise Virtual best-in-class logical switch solution features:

  • The high availability and flexibility required in campus networks
  • A unified management and control plane
  • Faster convergence and higher throughput via an active-active data plane
  • Greater deployment flexibility with the introduction of a fiber port
  • Standard-based discovery
  • Future support of StackWise Virtual links in the cloud

So, with Cisco Next Generation StackWise Virtual solution, virtual stacking is set to become a best practice within enterprises. It simplifies network operations with a single control and management plane. It provides faster convergence for multicast and failover. It contributes to a more resilient network where system bandwidth can be scaled across a distributed forwarding plane. And now, system admins are free of the constraints of space and cables to deploy switches anywhere on optical fiber.

Enjoy more recent Cisco IOS XE Blogs:

High Availability – Features in Cisco IOS XE Software Makes It Appear Seamless
Cisco Champions the Powerful, Evolving Networking Software Stack
Enabling Scalable Group Policy with TrustSec Across Networks to Provide More Reliability and Determinism


Subrat Mohanty

Principal Software Engineer

Enterprise Networking Group