cisco帧中继的INTF模式

官方配置指导：The Cisco Frame Relay switching feature can be used to support a Frame Relay network using only routers.  Two Cisco routers are configured as Frame Relay switches implementing a Network-to-Network Interface (NNI) between them. To enable communication between two Frame Relay switches, the NNI signaling protocol is used between them.

所以，当两台帧中继交换机上使用串行链路连接时，可以配置成帧中继封装，NNI模式是为了多台帧中继交换机交互用的，另外的DCE端为DTE端提供时钟频率。但是如果他们之间是以太网链路，就出现了帧中继和以太网都是二层导致冲突的情况，因此需要使用通用路由封装解决。