To be pedantic, the IMR provides object-key  IOR mappings. However, the object key used is part of an IOR that contained the IMR’s host and port, so conceptually the IMR provides IOR  IOR mappings.
A firewall is a part of security infrastructure that prevents malicious hackers on the Internet from accessing the computers inside an organization’s network. A firewall blocks most TCP/IP traffic from outside the organization’s network, but can be configured to allow traffic on a set of fixed ports. In this way, the firewall can be configured to allow external access to a small number of services that are inside the organization’s network; typical examples include FTP, telnet and/or a web server. A typical requirement for exposing an internal service through a firewall is that the service listen on a fixed port .