How to restrict remote connections to a Informix Instance but still allow the same users to access the database server locally.
Configure the Informix dbserver to use shared memory connections only. This will allow access by a local user, but that same user will not be able to access the database from another host, or client, workstation, etc using a network access.
The following example shows a sqlhosts entry for a shared memory connection
#dbservername nettype hostname servicename options
mydbsvr onipcshm myhostname mydbsvr