MPLS Ping

In Figure 1, an LSP destined for Router D is configured on Router A. The MPLS ping process on Router A is as follows:

1. Router A checks whether the LSP is established. If the LSP is a TE tunnel, Router A checks whether the tunnel interface is configured and the CR-LSP is established. If the LSP is not established, an error code is displayed, and the MPLS ping process ends. If the LSP has been established, the MPLS ping process continues.
2. Router A constructs an MPLS Echo Request message, with destination IP address 127.0.0.0/8 and TTL value 1 in the IP header. Then, Router A adds an LSP label to the MPLS Echo Request message and sends the message to Router B.
3. Transit nodes Router B and Router C forward this MPLS Echo Request message using MPLS. If either transit node fails to forward the MPLS Echo Request message, this message is discarded.
4. If MPLS forwarding is successful, the MPLS Echo Request message reaches the egress Router D, and the Router D replies with an MPLS Echo Reply message to Router A.