This read-write switch enables or disables the "TCP Syn and Fin" Denial-of-Service protection feature, which detects TCP packets that have both the SYN and FIN flags set simultaneously. Admins enable it because a packet with SYN and FIN both set is invalid under normal TCP semantics, since a connection can't be opening and closing at once, making it a well-known scanning or crafted-packet signature. For example, enabling this causes the switch to drop a SYN+FIN packet often used by port scanners attempting to evade basic filtering.