问答题
我们在日常工作中通常使用show interface[端口及端口号]来查看端口的运行状态，下面的例子是在不同情况下看到的端口状态行的内容，请分析其产生的原因及解决方法。 1. Router # show interface serial 0 Serial0 is up, line protocol is up
Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of show interface counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 1000 hits/sec, 2 packets/sec 5 minute output rate 1000 bits/sec, 2 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 0 packets output, 0 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 last carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out 2. Router # show interface serial 0 Serial0 is down, line protocol is down Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of show interface counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 1000 bits/sec, 2 packets/sec 5 minute output rate 1000 bits/sec, 2 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giant】s, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 0 packets output, 0 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 last carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out 3. Router # 4 show interface serial 0 Serial0 is up, line protocol is down Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output hang never Last clearing of show interface counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 1000 bits/sec, 2 packets/sec 5 minute output rate 1000 bits/sec, 2 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 0 packets output, 0 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out 4. Router # show interface serial 0 Serial0 is administratively down, line protocol is down Hardware is HD64570 MTU 1500 bytes, BW 1544 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:00:00, output 00:00:00, output bang never Last clearing of show interface counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops 5 minute input rate 1000 bits/sec, 2 packets/sec 5 minute output rate 1000 bits/sec, 2 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 0 packets output, 0 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
【正确答案】若是"Serial0 is up，line protocol is up．"表示该端口工作正常。 (2)若是"Serial 0 is down，line protocol is down．"表示路由器到本地的Modem之间无载波信号CD。连接串口和Modem，开启Modem。看Modem的发送灯TD是否亮，TD灯亮表示路由器有信号发送给Modem。TD灯若不亮，请检查Modem，线缆(最好用Cisco所配的)和端口。也可以用另外一个串口试试。 (3)若Serial is up，但 line protocol is down有几种可能： ●本地路由器未作配置。 ●远端路由器未开或未配置。 路由器两端需要配置相同的协议打包方式。例如：路由器A打包HDLC，路由器B打包 PPP，那么两台路由器的line protocol始终是down的。改变打包方式： Router # conf t Router(config) # interface serial 0 Router(config-if) # encapsulation ppp Router(config-if) #^Z Router# ●若是使用Newbridge的26XX，27XX的DTU设备，它不发送CD信号，在路由器上设置如下： Router # configure terminal Router(config) # int serial 0 Router(config-if) # ignored-dcd Router(config-if) #^Z Router# ●Modem之间没通，即专线没通。 解决办法：作测试环路。请电信局帮助确定具体出现问题是哪一段线路。若作环路成功， line protocol会变成up(looped)。 (4)若"Serial is admsinstratively down，line protocol is down．"表示端口管理性关闭。在该端口做以下工作： Router # conf t Router(config) # interface serial 0 Router(config-if) # no shutdown Router(config-if) #^Z Router#