Contact a Nokia technical support representative for scaling information about the minimum and maximum number of nodes supported in the VC.
The nodes in a VC are modeled in software as either CPM nodes or IMM nodes. The CPMs and the IMMs are interconnected through stacking ports.
In a VC, CPMs perform a dual role and will also act as IMMs. Consequently, a CPM is referred to as a CPM-IMM node and the IMM is referred to as an IMM-only node. Nodes in a VC are IMM-only nodes by default, but an IMM-only node is not mandatory in a VC.
If only one node is configured in the VC (minimum requirement), it must be a CPM-IMM node. A maximum of two CPM-IMM nodes can be configured on the VC to provide control plane redundancy. In this case, the remaining nodes must be IMM nodes. If more than two CPM-IMM nodes are configured, the software logs an error. The user can also configure a VC with one CPM-IMM and one IMM-only node; however, this configuration does not provide control-plane redundancy.
During the boot process, the system designates one of the configured CPM-IMM nodes as the active and the other as the standby CPM-IMM. If the active CPM-IMM fails, the standby CPM-IMM takes over the active role. It is possible to upgrade an existing IMM-only node to be a CPM-IMM node so that if an existing CPM-IMM node fails, another node can take on its role. See Configuration guidelines for upgrading, adding, or removing a VC node for more information about upgrading an IMM-only node to a CPM-IMM node. It is also possible to add a new node to the VC as a CPM-IMM node in the event that an existing CPM-IMM node must be replaced; however, there are restrictions. See Permitted platform combinations in a VC for more information. For information about adding and removing nodes in different scenarios, see VC boot scenarios.