This read-only field reports the actual real-time operational state of ILMI on this port, down, not functioning, registering, in the process of exchanging initial ILMI information with the peer, or up, fully operational, reflecting what is really happening as opposed to the administrative on/off setting in lportIlmiAdminStatus. An admin checks this when troubleshooting an ATM port that seems otherwise fine but exhibits configuration-discovery issues, since a port stuck at registering rather than reaching up indicates the ILMI handshake with the peer is not completing. For example, lportIlmiOperStatus stuck at registering(2) despite lportIlmiAdminStatus being enabled would suggest the connected device is attempting ILMI but the exchange is not successfully completing, worth checking against lportIlmiPollTimeout and lportIlmiPollRetry settings.