This read-only enumerated value reports whether the switch generates an unknown-address notification message when it receives traffic for a destination not present in its Fast Forwarding Table. An administrator checks this to understand whether such unknown-destination events are signaled anywhere, which affects troubleshooting visibility for forwarding-cache misses. For example, if rlIpFftUnknownAddrMsgUsed reports used, the admin knows the device raises some form of message when traffic hits an FFT cache miss, which can be useful for diagnosing forwarding gaps.