Attacks　executed　on　Spanning　Tree　Protocol　(STP)　expose　the　weakness　of　link　layer　protocols　and　put　the　higher　layers　in　jeopardy.　Although　the　problems　have　been　studied　for　many　years　and　various　solutions　have　been　proposed,　many　security　issues　remain.　To　enhance　the　security　and　credibility　of　layer-2　network,　we　propose　a　trust-based　spanning　tree　protocol　aiming　at　achieving　a　higher　credibility　of　LAN　switch　with　a　simple　and　lightweight　authentication　mechanism.　If　correctly　implemented　in　each　trusted　switch,　the　authentication　of　trust-based　STP　can　guarantee　the　credibility　of　topology　information　that　is　announced　to　other　switch　in　the　LAN.　To　verify　the　enforcement　of　the　trusted　protocol,　we　present　a　new　credible　evaluation　method　of　the　STP　using　a　specification-based　state　model.　We　implement　a　prototype　of　trust-based　STP　to　investigate　its　practicality.　Experiment　shows　that　the　trusted　protocol　can　achieve　security　goals　and　effectively　avoid　STP　attacks　with　a　lower　computation　overhead　and　good　convergence　performance.