Responder node procedures

The following are responder node procedures:

1. As a responder node, the node will always insert a global return code return code of either 3 Replying router is an egress for the FEC at stack-depth <RSC> or 14 See DDMAP TLV for Return Code and Return Subcode.

2. When the responder node inserts a global return code of 3, it will not include a DDMAP TLV.

3. When the responder node includes the DDMAP TLV, it inserts a global return code 14 See DDMAP TLV for Return Code and Return Subcode and:

   1. On a success response, include a return code of 15 in the DDMAP TLV for each downstream which has a FEC stack change TLV.

   2. On a success response, include a return code 8 Label switched at stack-depth <RSC> in the DDMAP TLV for each downstream if no FEC stack change sub-TLV is present.

   3. On a failure response, include an appropriate error return code in the DDMAP TLV for each downstream.

4. A tunneling node indicates that it is pushing a FEC (the tunneling FEC) on top of the target FEC stack TLV by including a FEC stack change sub-TLV in the DDMAP TLV with a FEC operation type value of PUSH. It also includes a return code 15 Label switched with FEC change. The downstream interface address and downstream IP address fields of the DDMAP TLV are populated for the pushed FEC. The remote peer address field in the FEC stack change sub-TLV is populated with the address of the control plane peer for the pushed FEC. The Label stack sub-TLV provides the full label stack over the downstream interface.

5. A node that is stitching a FEC indicates that it is performing a POP operation for the stitched FEC followed by a PUSH operation for the stitching FEC and potentially one PUSH operation for the transport tunnel FEC. It will therefore include two or more FEC stack change sub-TLVs in the DDMAP TLV in the echo reply message. It also includes and a return code 15 Label switched with FEC change. The downstream interface address and downstream address fields of the DDMAP TLV are populated for the stitching FEC. The remote peer address field in the FEC stack change sub-TLV of type POP is populated with a null value (0.0.0.0). The remote peer address field in the FEC stack change sub-TLV of type PUSH is populated with the address of the control plane peer for the tunneling FEC. The Label stack sub-TLV provides the full label stack over the downstream interface.

6. If the responder node is the egress for one or more FECs in the target FEC Stack, then it must reply with no DDMAP TLV and with a return code 3 Replying router is an egress for the FEC at stack-depth <RSC>. RSC must be set to the depth of the topmost FEC.

   This operation is iterative in the sense that, at the receipt of the echo reply message, the sender node will pop the topmost FEC from the target stack FEC TLV and resend the echo request message with the same TTL value as described in step 5 as follows. The responder node will therefore perform exactly the same operation as described in this step until all FECs are popped or until the topmost FEC in the target FEC stack TLV matches the tunneled or stitched FEC. In the latter case, processing of the target FEC stack TLV follows again steps 1 or 2.