Fault Symptom
Router A and Router B are connected by using an MP-group interface consisting of two CE1 interfaces. All timeslots of each CE1 interface are bundled into a synchronous serial interface to transmit services.
After the link of CE1 1/0/0 fails, 50% packets are dropped in the first minute, and the link recovers and no packet is dropped in two minutes.
Fault Analysis
After an MP-group member link becomes unavailable, the traffic transmitted over this link automatically switches to the other available link.
In addition, a PPP-enabled router sets the PPP status of the link to Down after failing to receive 10 consecutive Hold time messages.
A Hold time message is sent every 10 seconds by default, and it takes 100s to send 10 Hold time packets. This is why the peer router can detect that the link is Down about two minutes (100s) after the PPP status is set down.
Router B continues to send messages along the failed link 100s after the failure occurs. As a result, half of packets are dropped during this period of time. After Router A sets the PPP status to Down, Router B detects that the link goes Down and no longer sends messages along the failed link, and thus no message is dropped.
You can set a shorter interval at which a Hold time message is sent to rectify the fault.
Run the following commands on two routers on the two ends of the PPP link:
Procedure
1. Run the system-view command to enter the system view.
2. Run the interface serial 1/0/0:0 command to enter the view of the synchronous serial interface composed of CE1 interfaces.
3. Run the timer hold 1 command to set the interval at which a Hold time message is sent to 1 second.
4. Run the shutdown and undo shutdown commands to restart the CE1 interface.
After the configurations, run the ping command on Router A or Router B to ping the peer. No packet is dropped. The fault is then rectified.
Summary
Set a smaller interval at which a Hold time message is sent on both ends of a PPP link, enabling a rapid response to the link status change on an unstable network.
