Restricting users connecting from a certain host

Hi, I would like to know whether an Informix 7.X server running on Linux would be able to accept or reject a connection coming from a particular host depending on the user name supplied. The scenario is as follows. We want to setup an Informix database server behind a firewall. The server should accept all connections coming from the local network. However, we'd like to restrict the access from hosts outside the local network. We can easily do that configuring the firewall in a way that it rejects all connections to the port Informix is listening to. However, there's a particular host outside the firewall that should access the database. We would like to find the way of accepting connections to the database coming from that host, but only for a particular username (a user name that would be granted read privileges only). All attempts from other users in that host should be rejected. Is it possible? Thanks in advance, and apologies for my ban English. Guillermo Labatte