The control information on a physical switch is normally transparent to the network module. This internal network is isolated by design. However, the N1KV control packets need to traverse the physical network between the VSM and the VEM.

Cisco N1KV uses the Domain ID to identify a VSM and a VEM for ease of relating to one another, so that the VEM only receives the control packets intended for it and from the correct VSM. An SA defines this ID at the time of the VSM installation, and becomes a part of the opaque data that is transmitted to vCenter.

This concept is depicted in the following diagram: