are the 172.x.y.z nodes behind a NAT (hence the communication back
isn't possible - only the stdout from the rsh/ssh is working in this
case)?

-- Reuti

Actually I dont know  exactly , I am asking  extra informations to my network architect
Interesting thing to notice is that LAM  worked in such kind of  network configuration.
I keep you inform as soon as I have more infos.
 

Regards
Geoffroy