Oracle Application Server NameServer Internet Inter-ORB Protocol (IIOP) is used in distributed computing based on CORBA (Common Object Request Broker Architecture). Even though CORBA and IIOP are OMG standards, no fixed port is assigned for IIOP. Each vendor implementing CORBA chooses a port. Java Virtual machine uses port 1975 by default, while ORBIX uses 3075 by default.
The IIOP ALG monitors the control packets, dynamically opens flows, and performs NAT address and port rewrites.