R2630 router Serial00 protocol layer cannot be up. Close it and restart it, the physical layer and protocol layer are up and the service is normal. Several minutes later the protocol layer is down.
Enter interface view and use no keepalive
% Line protocol ip on interface Serial00, changed state to UP
The problem is solved.
1. The physical layer is up.
2. Check port state and find:
Encapsulation HDLC, keepalive set (10 sec)
Input keepalive packages0, Output keepalive packages15879
The interface only sends Keepalive packet and does not receive Keepalive packet.
3. The reason is that Keepalive timer is timeout.
If Keepalive timer configuration of two ports is different, similar problem may occur. If detailed reason cannot be checked, not use Keepalive timer to avoid it.