VSI Master and VSI Slaves

The VSI separates the networking application from the switch-specific software. The networking application includes a VSI master module, and the switch includes one or more VSI slave modules.

Although there's only one VSI master per controller, there can be one or more VSI slaves in the controlled switch. The VSI slaves can be classified as centralized, distributed, and hybrid.

In the centralized model, shown in Figure 2-4, a single VSI slave process is running on the switch control card. It controls all the interfaces in the switch. The VSI master interfaces with only one VSI slave process. The switch's resource management is centralized. This model is also called the proxy VSI slave because it handles the slave functionality for the interface cards.

Figure 2-4. VSI Slaves: Centralized Model

In the distributed model, shown in Figure 2-5, each card has its own VSI slave process, so several VSI slave processes are running in the switch. These cards have more intelligence than the cards in the centralized model. Resource management and connection setup and teardown run on the processors on the service cards.

Figure 2-5. VSI Slaves: Distributed Model

The controller card does not take part in connection control; it performs configuration management operation.

Connection requests from the VSI master might need to be performed with two slaves to set up the two legs of the cross-connects.

The last model, shown in Figure 2-6, is a combination of the previous two models. It can be seen as a special kind of distributed model. The control card controls interfaces on some cards, and other cards run their own VSI slave process.

Figure 2-6. VSI Slaves: Hybrid Model

From a different angle, a switch controlled by multiple controllers using VSI looks like Figure 2-7.

Figure 2-7. Multiple Controllers

Each controller uses a different controller-id when communicating with the slave(s).

There is no requirement for master-to-master communication. Resources in the switch are managed by the platform software, reinforcing the "ships in the night" concept.