Fault Symptom
RouterA functions as the egress of the network and accesses the Internet through RouterB. RouterA and RouterB intercommunicate through an MP-group link on which there is a transmission device. An MP-group link is formed by bundling eight CE1 links.
When a user attached to RouterA accesses the Internet, the DNS server sometimes cannot be pinged successfully; the long delay of packets and packet loss may frequently occur; the webpage sometimes cannot be accessed.
Fault Analysis
1. On the transmission device, check the status of the physical interface and optical fiber. The physical interface and optical fiber are detected normal.
2. On RouterA and RouterB, run the display interface command to view information about the MP-group interface and its member interfaces.
Check the following information:
· Whether the interface becomes Up
· Whether the clock mode is correct
· Whether the line coding/decoding formats on both ends are consistent
· Whether loopback is configured
· Whether alarms are generated
[RouterA] display controller e1 1/0/0
E1 1/0/0 current state : UP
Description : E1 1/0/0 Interface
Physical layer is Packet Over NO-CRC4
clock slave, linecode hdb3 , loopback none
section layer:
alarm: LOS
line layer:
alarm: none
path layer:
alarm: none
[RouterB] display controller e1 1/0/0
E1 1/0/0 current state : UP
Description : E1 1/0/0 Interface
Physical layer is Packet Over NO-CRC4
clock master, linecode hdb3 , loopback none
section layer:
alarm: LOS
line layer:
alarm: none
path layer:
alarm: none
When a transmission device is on the link, the router needs to obtain clock signals from the transmission device, which requires the router to work in slave clock mode.
The CE1 interface on RouterA is configured to work in slave clock mode, whereas the CE1 interface on RouterB is configured to work in master clock mode. Therefore, the link is unstable due to incorrect clock configuration.
Procedure
1. Run the system-view command on RouterB to enter the system view.
2. Run the controller e1 1/0/0 command to enter the CE 1 interface view.
3. Run the clock slave command to change the clock mode of the CE1 interface to the slave clock mode.
4. Configure the same on each member interface of the MP-group interface.
Check the status of the CE1 interfaces on the routers on both ends. You can find that the link is stable and packets can be transmitted and received normally. The fault is rectified.
Summary
Functioning as the synchronous interface, the CE1 interface can work in data terminal equipment (DTE) mode and data circuit-terminating equipment (DCE) mode. In addition, the interface requires a clock mode.
On the CE1 interface, you can select one of the following clock modes:
· Master clock mode: uses the internal clock signal.
· Slave clock mode: uses the line clock signal.
When the CE1 interfaces of two devices are directly connected, one interface should be configured to work in master clock mode and the other interface should be configured to work in slave clock mode.
When the CE1 interface of a device is connected to a transmission device, the CE1 interface must be configured to work in salve clock mode and obtains clock signals from the transmission device.
