does the ping work from AS/400 when using the ip-adress ? What did you enter in the command CHGTCPDMN (cfgtcp option 12) ? Is there perhaps no DNS-Server entered ? This would explain this behaviour. When you want to add one, please use HOSTSCHPTY *LOCAL because of performance reasons. Then the hosts of the AS/400 (cfgtcp option 10) will be searched first and only when this doesn't work, the DNS-server is asked.