Not able to connect to node manager because of Connection refused: connect

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Applies to:
Weblogic Server: 10.3.6 and later
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Problem Summary:
We are trying to connect to node manager to perform restart using nmConnect but couldn't able to.

Error:
wls:/offline> nmConnect('weblogic','weblogic123','localhost','25000','weblogic_poc_dit')
Connecting to Node Manager ...
Traceback (innermost last):
  File "<console>", line 1, in ?
  File "<iostream>", line 123, in nmConnect
  File "<iostream>", line 648, in raiseWLSTException
WLSTException: Error occured while performing nmConnect : Cannot connect to Node
 Manager. : Connection refused: connect. Could not connect to NodeManager. Check
 that it is running at localhost:25000.
Use dumpStack() to view the full stacktrace
wls:/offline>
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Root Cause:
Node manager isn't running at localhost:25000 becuase of which connection is refused.
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How to verify:
1. Login to localhost
2. Use /usr/sbin/lsof -i:25000 or ps -ef | grep weblogic.NodeManager command to verify if node manager is up and running.
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Resolution:
1. Go to $DOMAIN_HOME/bin and start node manager using startNodeManager.sh
<Feb 11, 2017 12:29:20 PM CST> <INFO> <Secure socket listener started on port 25000, host localhost/192.168.184.130>
2. Once it is started listening, try to connect to node manager using nmConnect
wls:/offline> nmConnect('weblogic','weblogic123','localhost','25000','weblogic_poc_dit')
Connecting to Node Manager ...
Successfully Connected to Node Manager.
wls:/nm/weblogic_poc_dit>