One NE80E router working as edge router in MPLS domain, suddenly all the LDP session went down, due to which all the traffic forwarding through this router affected.
Step 1. Checked the physical state of all interfaces on which MPLS LDP was running, and found that all interfaces were in up state.
Step 2. Checked the IGP routing table for the routes to LDP peers and found that routes were present.
Step 3. Checked the current configuration for MPLS and found that command MPLS LDP was not configured in config mode. Then we checked the logs and found that Customer engineer run the command "undo mpls ldp" in config mode, due to which all LDP sessions went down immediately.Later when discussed this with customer, we came to know that customer wanted to remove ldp from one interface and they removed it from global by mistake.
This problem maybe caused by following reasons:
1. The interfaces on which the LDP session is established is shut down.
2. No route exists in IGP routing table.
3. Customer undo mpls, undo mpls ldp, or undo mpls ldp remote peer command is run.
The engineer working at configuration level should be well qualified and must have a good knowledge on the product and technology on which they are working. If they dont know about configuration and need to make some changes, customer should immediately contact Huawei support.