填空题 12.  If ______ are needed，you should either deploy a completely redundant network path that is under the control of local administration or use multiple-transport networks(two ISPs)and connect them to either redundant interfaces or redundant VPN devices. 如果要求建立______，那么你可以在本地管理范围之内的传输网络上建立完全冗余的网络路径，或是启用多个传输网络(如两个ISP)并使用冗余接口或冗余VPN设备进行连接。