EFM OAM and line loopback are mutually exclusive. If one of these functions is enabled, it must be disabled before the other can be used.
However, a line loopback precedes the dot1x behavior. That is, if the port is already dot1x-authenticated it will remain so. If it is not, EAP authentication will fail.
Ethernet port-layer line loopback and Ethernet port-layer internal loopback can be enabled on the same port with the down-when-looped feature. EFM OAM cannot be enabled on the same port with the down-when-looped feature. For more information, see Ethernet Port Down-When-Looped.