This specifies whether a specific monitored VLLI instance is tracking a physical port's link status or a CFM connectivity-fault-management session's continuity-check state as its fault-detection mechanism, which determines what kind of failure this instance can actually detect. An admin monitoring an Ethernet virtual circuit that spans multiple hops, where a simple physical link-down check on the local port wouldn't reveal a failure elsewhere in the path, would configure the instance type as cfm to rely on end-to-end continuity checks instead of local link state. For example, a pseudowire endpoint that stays physically up even when the far end fails would need a cfm-type instance to actually detect that remote failure, since a port-type instance would see nothing wrong locally.