ND snooping commands clear nd-snooping binding 明确nd-snooping statistics nd-snooping nd-snooping(inconfig-vlancontext) nd-snooping mac-check nd-snooping prefix-list nd-snooping max-bindings nd-snooping nd-guard nd-snooping ra-guard nd-snooping ra-drop nd-snooping trust show nd-snooping show nd-snooping binding 显示nd-snooping prefix-list show nd-snooping statistics