网络说明：

1、X，Y都是路由器。

2、A，B是一般的协议转换器。在上面有一些打环的按钮。

3、X到A一般通过是V24或V35线缆，

4、A到B一般是光纤，租用电信的，这一部分就是电信打环时能确认电信哪端线路是否是好用的。   注意：电信只会给你确认A—B段线路是否好的。

打环测试

第一步

1、<X>reset count interface

  或[X]reset count interface

2、在X端口上打环。

       [X-Serial2/1]loopback

   过几十秒后

       <X>dis int s 2/1  

Serial2/1 current state :UP  

Line protocol current state :DOWN

Description :  Serial2/1 Interface

The Maximum Transmit Unit is 1500, Hold timer is 10(sec)

Internet Address is 192.168.2.2/24

Link layer protocol is PPP, loopback is detected 

LCP closed

Output queue : (Urgent queue : Size/Length/Discards)  0/50/0

Output queue : (Protocol queue : Size/Length/Discards) 0/500/0

Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0

Physical layer is synchronous, Loopback,Baudrate is 64000 bps

Interface is DCE, Cable type is V35

    Last 300 seconds input rate 0.00 bytes/sec, 0.00 packets/sec

    Last 300 seconds output rate 0.00 bytes/sec, 0.00 packets/sec

    Input: 22 packets, 336 bytes   Input 和Output 的都相等。

           0 broadcasts, 0 multicasts

           0 errors, 0 runts, 0 giants

           0 CRC, 0 align errors, 0 overruns

           0 dribbles, 0 aborts, 0 no buffers

           0 frame errors

    Output:22 packets, 336 bytes

           0 errors, 0 underruns, 0 collisions

           0 deferred                    

DCD=UP  DTR=UP  DSR=UP  RTS=UP  CTS=UP 

结论：端口是好的。模块没有问题。

第二步

1、在端口上去掉打环。

       [X-Serial2/1]loopback

2、在A光电转换器上打本地环。

   过几十秒后

<X>dis int s 2/1  

Serial2/1 current state :UP  

Line protocol current state :DOWN

Description :  Serial2/1 Interface

The Maximum Transmit Unit is 1500, Hold timer is 10(sec)

Internet Address is 192.168.2.2/24

Link layer protocol is PPP, loopback is detected 

LCP closed

Output queue : (Urgent queue : Size/Length/Discards)  0/50/0

Output queue : (Protocol queue : Size/Length/Discards) 0/500/0

Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0

Physical layer is synchronous, Loopback,Baudrate is 64000 bps

Interface is DCE, Cable type is V35

    Last 300 seconds input rate 0.00 bytes/sec, 0.00 packets/sec

    Last 300 seconds output rate 0.00 bytes/sec, 0.00 packets/sec

    Input: 55 packets, 840 bytes   Input 和Output 的都相等。

           0 broadcasts, 0 multicasts

           0 errors, 0 runts, 0 giants

           0 CRC, 0 align errors, 0 overruns

           0 dribbles, 0 aborts, 0 no buffers

           0 frame errors

    Output:55 packets, 840 bytes

           0 errors, 0 underruns, 0 collisions

           0 deferred                    

DCD=UP  DTR=UP  DSR=UP  RTS=UP  CTS=UP 

结论：从端口到A的本地线缆是好的。

第三步

1、在A光电转换器去掉打环。

2、在B光电转换器上打远程环。

   过几十秒后

<X>dis int s 2/1  

Serial2/1 current state :UP  

Line protocol current state :DOWN

Description :  Serial2/1 Interface

The Maximum Transmit Unit is 1500, Hold timer is 10(sec)

Internet Address is 192.168.2.2/24

Link layer protocol is PPP, loopback is detected 

LCP closed

Output queue : (Urgent queue : Size/Length/Discards)  0/50/0

Output queue : (Protocol queue : Size/Length/Discards) 0/500/0

Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0

Physical layer is synchronous, Loopback,Baudrate is 64000 bps

Interface is DCE, Cable type is V35

    Last 300 seconds input rate 0.00 bytes/sec, 0.00 packets/sec

    Last 300 seconds output rate 0.00 bytes/sec, 0.00 packets/sec

    Input: 77 packets, 1176 bytes   Input 和Output 的都相等。

           0 broadcasts, 0 multicasts

           0 errors, 0 runts, 0 giants

           0 CRC, 0 align errors, 0 overruns

           0 dribbles, 0 aborts, 0 no buffers

           0 frame errors

    Output:77 packets, 1176 bytes

           0 errors, 0 underruns, 0 collisions

           0 deferred                     

DCD=UP  DTR=UP  DSR=UP  RTS=UP  CTS=UP 

结论：从端口到B的线缆是好的。

第四步

1、在B光电转换器去掉打环。

2、在Y上的。

[Y-Sierial2]loopback

   过几十秒后看X路由器

<X>dis int s 2/1  

Serial2/1 current state :UP  

Line protocol current state :DOWN

Description :  Serial2/1 Interface

The Maximum Transmit Unit is 1500, Hold timer is 10(sec)

Internet Address is 192.168.2.2/24

Link layer protocol is PPP, loopback is detected 

LCP closed

Output queue : (Urgent queue : Size/Length/Discards)  0/50/0

Output queue : (Protocol queue : Size/Length/Discards) 0/500/0

Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0

Physical layer is synchronous, Loopback,Baudrate is 64000 bps

Interface is DCE, Cable type is V35

    Last 300 seconds input rate 0.00 bytes/sec, 0.00 packets/sec

    Last 300 seconds output rate 0.00 bytes/sec, 0.00 packets/sec

    Input: 99 packets, 1512 bytes   Input 和Output 的不相等。

           0 broadcasts, 0 multicasts

           0 errors, 0 runts, 0 giants

           0 CRC, 0 align errors, 0 overruns

           0 dribbles, 0 aborts, 0 no buffers

           0 frame errors

    Output:87 packets, 1480 bytes

           10 errors, 0 underruns, 0 collisions

           0 deferred                    

DCD=UP  DTR=UP  DSR=UP  RTS=UP  CTS=UP 

结论：说明路由器Y到B的线路有问题。