The status of a node will be "unknown" when the dmgr is unable to communciate with the node. In this example, at System Administration > Nodes in the dmgr, the status of the node named was1 is unknown.

The most obvious thing that will cause the status of a node to be unknown is that the node is stopped. If the node is stopped, start the node.

If the node is running and the status remains unknown, there may be a firewall between your dmgr and node server, such as iptable or firewalld (Linux), and the SOAP port and CELL_DISCOVERY_ADDRESS ports are not opened in the firewall. To determine the SOAP_CONNECTOR_ADDRESS and CELL_DISCOVERY_ADDRESS ports, navigate to System administration > Deployment manager > Ports. In this example, the CELL_DISCOVERY_ADDRESS port is 7277 and the SOAP_CONNECTOR_ADDRESS port is 8879. If you have to update your firewall to allow access to the SOAP port and CELL_DISCOVERY_ADRESS port, you will probably need to restart the dgmr. Cell discovery is how the dmgr discovers the node agent.

If the status remains unknown, check the node agent HPEL or SystemOut.log for event HMGR0149E. If this event is in the log, refer to this article.

HMGR0149E: An attempt to open a connection to core group DefaultCoreGroup has been rejected.
The sending process has a name of your_cell\your_node\dmgr and an IP address of x.x.x.x.
Global security in the local process is Enabled.
Global security in the sending process is Enabled.
The received token starts with ??????^[^K?<?P?.?)^X^Y-??DQ.
The exception is com.ibm.websphere.security.auth.WSLoginFailedException: Validation of LTPA token failed due to invalid key or token type.