Rules for Creating Links and Interface Overprovisioning¶
While you can create or redirect links even when the nodes involved in the link are running as part of a simulation, it is only possible to create a link if the nodes at either end of the link each have an unused interface available. Once a node has been started, the number of interfaces allocated to that node cannot be changed until the node is stopped and wiped. This restriction means that link creation and interface creation behave differently once you have started a node.
If you add a node to the canvas and have not started it yet, or if you have wiped a node and not started since wiping it, the Workbench automatically adds additional interfaces to a node to accommodate new links. You may also add extra interfaces directly to a node. Each node definition has a maximum possible number of interfaces. If the node is not at the maximum number of allocated interfaces for its node definition, you can select it as the source or target of a link. If all of the allocated interfaces are used by existing links, the Workbench permits you to select an unallocated interface for the connection, and it allocates that interface to the node when you create the connection. If the node already has its maximum number of interfaces allocated, and all of the interfaces are in use, then it is not possible to create a new link with that node.
If a node is currently running as part of a simulation, or if the node is stopped but has associated simulation state that has not been wiped, then the number of interfaces allocated to that node cannot be changed. If at least one of the interfaces allocated to the node is unused, then you can select it as the source or target of a link. If all of the interfaces allocated to the node are used by existing links, then it is not possible to create a new link with that node even if the node has fewer allocated interfaces than its maximum number of allowed interfaces. Before you can add a link or interface to such a node, you must stop and wipe the node.
Tip
To avoid having to stop a node in your simulation or to recreate its state after wiping it, you may want to overprovision interfaces on the nodes in your labs. Overprovisioning interfaces means allocating more interfaces on a node than it needs for the existing links in the topology. If you overprovision the interfaces on the nodes in your lab, each node has at least one unused interface when you first start the simulation. These extra interfaces enable you to add additional nodes and links to your lab later without having to stop or wipe any of the existing nodes in the lab.
Because interfaces consume system resources, CML only allocates additional interfaces to a node when the interfaces are needed for a new link. Each node definition has a default initial number of interfaces. When you first drag-and-drop a node into the lab, the node will have the default number of interfaces allocated to it. In smaller topologies, the default number of interfaces may create some modest overprovisioning, but if you want to overprovision interfaces in your lab, you should check all nodes before starting the lab to ensure that each one has enough unused interfaces allocated to each node.
Tip
If you cannot create a connection to a node, select the node and then click the Interfaces tab in the lower pane of the Workbench. If the button in the top-left of the Interfaces pane indicates Max Interfaces Reached, then the node has reached the maximum number of interfaces possible for that node type. If the button is disabled but indicates Add # Interfaces, then additional interfaces can be added to the node, but the node must be stopped and wiped first.