Is Informix aware of NIS included users

Hello, is informix aware of users which are not local users on the server where the sqlexecd is running but are included via NIS. ?? It seems not because i always get a 952 error. User is on machine C and starts dbaccess. He wants to connect not the local infse@machineA (setting of INFORMIXSERVER variable) but to the infse@machineB server. He goes to the connection dialogue and chooses the infse@machineB connection and then typing in the requested username and password. This is however not a lokal user on machine B but a NIS user (and the server is on machine A). He always got error 952. I traced the sqlexed on machineB. When the user tries to connect, there is a conversion between machineB and the ypserv on machineC. But something seems to be wrong as the user is reported as not existing. Strange. When the user logs into machine B directly and accesses infse@machineB everthing is working. both machines A and B are running linux (2.2.10 kernel and 2.0.30 kernel) and informix SE 7.2x. Do i have to put machine C in the .rhosts file to get it working? Greetings, Joerg