MongoDB Replication Set Configuration Issue on CentOS 7
mongo --host 10.0.0.7/admin --port 27017 -u user -p mypassword


The above command takes 10.0.0.7 as replica set name and admin as the hostname. That is the reason you are getting the error.

Use any of the following commands to connect to your MongoDB database

mongo 10.0.0.7/admin --port 27017 -u user -p mypassword

mongo admin --host 10.0.0.7 --port 27017 -u user -p mypassword