2) ROOT-GUARD. Root guard for spanning tree can be used to prevent a certain switch from becoming the root bridge. Even if you receive a superior BPDU from another switch, root guard will prevent that switch from becoming the root bridge.at-IOS#(config-if)# spanning-tree guard root. Example of this: http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800ae96b.shtml. 3). BPDU Guard: We suggest you to enable bpduguard at the global level so that it gets automatically inherited to the port-fast/access port configuation.