You might want to control which network node is selected by an end node as its network node server (NNS). For example, you might want to exclude a particular network node from network node server responsibilities because acting as a server involves some overhead, such as originating search requests or executing domain broadcasts. You might also want to specify which network nodes should be allowed as backup network node servers in the event the primary network node server becomes unavailable.

You can use a network node server list to indicate the network nodes that can act as servers for an end node. An end node detects adjacent network nodes capable of acting as its network node server through link activation or system definition. If you do not use a network node server list, the adjacent network node chosen as an end node server is directly related to when the end node becomes aware of that particular network node, relative to other adjacent network nodes. Without a network node server list, an end node establishes a CP-CP session with the first such network node that it becomes aware of, and this network node acts as the end node server. There is no predictability in this scheme; it is all timing-dependent. Therefore, if you want the network node server list to be used, you need to activate the list before activating links to network nodes. The configuration list should have the network node server list as one of the first resources to activate.

Initially, a CP-CP-capable physical connection might be temporarily unavailable between an end node and the network node that you prefer to have as the end node primary network node server. This situation requires the end node to establish CP-CP sessions with a backup server specified by the network node server list or, if no network node server list has been defined, with the first network node it can activate a CP-CP capable physical connection with.

By specifying the name of the end node preferred network node server on the end node NNSPREF start option, you allow the end node to automatically switch CP-CP sessions from its current NNS to the preferred NNS when a CP-CP-capable connection to the preferred network node server becomes available.