我们可以用show interface serial 0/0命令检查一条链路的状态,如出现Serial 0/0 is up, line protocol is up字样,则表示工作正常;如出现serial 0/0 is up, line protocol is down字样,则表示端口无物理故障,但上层协议未通(IP、IPX、X25等,此时应查看路由器的配置命令,检查地址是否匹配);如出现Serial 0/0 is down, line protocol is down (disable) 字样,则表示端口出现物理性故障,此时应更换端口;如出现Serial 0/0 is down, line protocol is down字样,则表示DCE设备(Modem/DTU)未送来载波/时钟信号;如出现Serial 0/0 is administratively down, line protocol is down字样,则表示接口被人为地关闭,可在配置状态中interface_mode下去掉shutdown命令。