IIOP - Internet Inter-ORB Protocol

It is possible to configure most firewalls to pass IIOP.
This is an exception rather than the rule, most firewall administrators may be wary of doing so.
However, firewalls configured to allow IIOP communications are not widespread.
And even when a corporation allows IIOP to pass through, the details of configuring firewalls for this purpose may not be widely understood.

IIOP can be made to work over SSL connections, although such configurations are not in widespread use.