This read-write object indicates whether the port operates in spanning-tree fast-start mode, immediately entering the forwarding state on link-up rather than starting in the blocking state, useful when the port is known to connect to a single station that has problems waiting for normal spanning-tree operation. This is what's now more commonly known as PortFast: it skips the normal listening and learning delay of up to 30-50 seconds before forwarding starts, which is safe specifically because the port connects to a single end station rather than another bridge, since enabling it on a port that actually connects to another switch risks a temporary bridging loop before spanning tree can react. Enabling this on a port connected to a single desktop PC lets that PC get network access within a couple seconds of link-up, but enabling it on a port that's actually uplinked to another switch could allow a brief loop if that uplink is part of a redundant path.