Iptables: What ports need to be open for Client Access (AS/400)

[Budi Febrianto]

Hi, Recently I create a firewall in my company using RHL 8.0 with iptables. There are 3 zone, and I put AS/400 in DMZ zone.   Users using Client Access to access AS/400, and I only open port 23 (TELNET). Users can access it, but later they got drop (Log out), or message error about communication.   Is there any ports need to be open to access AS/400 with client access?   Right now, I open all ports for AS/400 and the users can access it normally without being droped.   Thanks.