Mongodb 3.6 new features

1.authenticationRestrictions

            Added authenticationRestrictions parameter to the db.createUser() and db.updateUser()methods to restrict database user connections to specified IP addresses.

2.replSetResizeOplog

           replSetResizeOplog New in version 3.6. The replSetResizeOplog dynamically resizes a replica set member’s oplog to satisfy the operational needs in a replica set. It bypasses the need to perform a maintenance operation to resize the oplog. The command may only be run against the admin database. This feature is only available for nodes running on the WiredTiger storage engine. If you are using the MMAPv1 storage engine, see Change the Size of the Oplog to follow the maintenance procedure. 

        Use the stats command to display the current oplog size, maxSize. For example:

         use local
         db.oplog.rs.stats().maxSize

To change the size, run the replSetResizeOplog, passing the desired size in megabytes as a parameter.

db.adminCommand({replSetResizeOplog:1, size: 16384})
{ "ok" : 1, "operationTime" : Timestamp(1500329291, 1) }
3.IP whitelisting 

 user creation 

use admin
db.createUser(
{
user: "dba",
pwd: "dba",
roles: ["root"],
authenticationRestrictions: [ {
clientSource: ["192.168.30.16"],
serverAddress: ["198.51.100.0"]
} ]
}
)