Sender node procedures

The following are sender node procedures:

1. 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. That is, one FEC is popped at most and one or more FECs are pushed as indicated.

2. If the echo reply message contains the return code 3 Replying router is an egress for the FEC at stack-depth <RSC>, then:

   1. 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 will cause this case to occur as per step 6 of the Responder node procedures.

   2. 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 this step will continue 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 2.a is performed. A responder node will cause this case to occur as per step 6 of the Responder node procedures.

   3. 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 2.a or 2.b preceding. A responder node will not cause this case to occur but a third party implementation may do.

3. As a sender node, the can accept an echo-reply message with the global return code of either 14 (with DDMAP TLV return code of 15 or 8), or15 and process correctly the FEC stack change TLV as per step 1 of the sender node procedures.

4. 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 therefore the responder node, which is the egress node, will still reply with return code 4 Replying router has no mapping for the FEC at stack- depth <RSC>. This case cannot be resolved with this feature.