This section describes sender-node behaviors.
If the echo reply message contains the return code 14 See DDMAP TLV for
Return Code and Return Subcode and the DDMAP TLV has a return
code 15 Label switched with FEC change, the sender node
adjusts the target FEC Stack TLV in the echo request message for the next value
of the TTL to reflect the operation on the current target FEC stack as indicated
in the FEC stack change sub-TLV received in the DDMAP TLV of the last echo reply
message. In other words, one FEC is popped at most and one or more FECs are
pushed as indicated.
If the echo reply message contains the return code 3 Replying router is
an egress for the FEC at stack-depth <RSC>, then:
If the value for the label stack depth specified in the Return Sub-Code (RSC) field is the same as the depth of current target FEC Stack TLV, then the sender node considers the trace operation complete and terminates it. A responder node causes this case to occur as per step (6) of the responder node procedures.
If the value for the label stack depth specified in the Return Sub-Code (RSC) field is different from the depth of the current target FEC Stack TLV, the sender node must continue the LSP trace with the same TTL value after adjusting the Target FEC Stack TLV by removing the top FEC. Note that this step continues iteratively until the value for the label stack depth specified in the Return Sub-Code (RSC) field is the same as the depth of current target FEC Stack TLV and in which case step (a) is performed. A responder node causes this case to occur as per step (6) of the responder node procedures.
If a DDMAP TLV with or without a FEC stack change sub-TLV is included, then the sender node must ignore it and processing is performed as per steps (a) or (b) above. A responder node does not cause this case to occur but a third party implementation may.
As a sender node, the router can accept an echo-reply message with the global return code of either 14 (with DDMAP TLV return code of 15 or 8), or 15 and process properly the FEC stack change TLV as per step (1) of the sender node procedures.
If an LSP ping is performed directly to the egress LER of the stitched FEC, there
is no DDMAP TLV included in the echo request message and the responder node,
which is the egress node, replies with return code 4 Replying router has
no mapping for the FEC at stack- depth <RSC>. This case
cannot be resolved with this feature.