Ping failure
Symptom
The physical layer of the interfaces and the line protocol are both UP, but when tested with the ping command, the two ends are mutually unreachable.
Solution
If IPOA is used, make sure the IP protocol address mapping is configured correctly. If the interfaces of two routers are connected back-to-back, the local PVC mapped to the remote IP must have the same VPI/VCI value as the remote PVC mapped to the local IP. In addition, the IP addresses of the two ends must also be in the same network segment.
If two routers are connected back-to-back, make sure at least one of interfaces uses internal transmission clock (master). Or, if the routers are connected to the ATM network, the transmission clock should be set to line clock.
Check the ATM interfaces of the two sides to make sure they are of the same type, for example, both are multimode fiber interfaces or both are single-mode fiber ports, or both are multi-mode fiber interfaces but connected using single mode. If a multimode fiber interface and a single-mode fiber interface are directly connected, they can communicate in most cases, but sometimes with frequent packet dropping and CRC errors.
If the two ends are PPPoA, make sure their IP addresses (should be in the same network segment) and authentication parameters are correctly configured.
If, according to the ping command, small packets can pass but big packets cannot, make sure the mtu configurations of the two router interfaces are the same.