This value reports the state of an interface's Link OAM parser, one of forward(1) for normal passthrough, loopback(2) meaning the interface is currently looping frames back (as used in remote-loopback testing), or discard(3) meaning frames are being dropped at the parser. A network administrator checks this to confirm whether an interface is stuck in loopback mode (which would explain unexpected connectivity behavior) or discarding frames due to an OAM issue. For example, seeing tnLOAMIfPARState as loopback(2) on a port an admin thought was in normal service would explain why end-user traffic on that port isn't reaching its destination.