MPLS LSP connectivity test when the initiator address is unknown

An apparatus comprising:

• a first edge label switching router element (LSR), the first edge LSR comprising:
• a first processor;
• and
• a first memory coupled to the first processor and configured to store first instructions executable by the first processor, wherein the first edge LSR is configured to implement a first method in response to execution of the first instructions, the first method comprising:
• detect receipt of a first echo request message, wherein
• the first echo request message is received by the first edge LSR on a label switch path (LSP),
• the first echo request is originated by an initiator;
• the first echo request message comprises a stack of one or more segment reachability (SR) sub-TLV (type-length-value) elements, each of which comprises an internet protocol (IP) address and a label allocated to reach the initiator;
• the first echo request message comprises an FEC (forwarding equivalence class) stack that identifies the LSP;
• detect a change in the FEC stack;
• in response to detecting the change in the FEC stack, generate a first SR sub-TLV element, wherein
• the first SR sub-TLV element comprises an internet protocol (IP) address of the first edge LSR and a first label allocated by the first edge LSR to reach the initiator;
• generate a first echo reply message that comprises a first stack of SR sub-TLV elements, which comprises the first SR sub-TLV element and a copy of the one or more SR sub-TLV elements of the first echo request message;
• attach one or more labels of the one or more SR sub-TLV elements to the first echo reply message;
• send the first echo reply message with the attached one or more labels towards the initiator;
• detect receipt of a second echo request message,
• the second echo request is originated by the initiator;
• the second echo request message comprises a plurality of SR sub-TLV elements, which includes the first SR sub-TLV element.

A non-transitory computer readable storage medium configured to store program instructions that, when executed on a processor, are configured to cause the processor to:

• detect receipt of an echo request message, wherein
• the echo request is originated by an initiator;
• the echo request message comprises a stack of one or more segment reachability (SR) sub-TLV (type-length-value) elements, each of which comprises an internet protocol (IP) address and a label allocated to reach the initiator;
• the first echo request message comprises an FEC (forwarding equivalence class) stack that identifies the LSP;
• detect a change in the FEC stack;
• in response to detecting the change in the FEC stack, generate a new SR sub-TLV element, wherein the new SR sub-TLV element comprises an internet protocol (IP) address of the LSR and a label allocated to reach the initiator;
• generate an echo reply message that comprises a new stack, which comprises the new SR sub-TLV element and a copy of the one or more SR sub-TLV elements from the echo request message;
• attach the one or more labels of the one or more SR sub-TLV elements to the echo reply message;
• forward the echo reply message toward the initiator with the attached one or more labels;
• detect receipt of a second echo request message,
• the second echo request is originated by the initiator;
• the second echo request message comprises a plurality of SR sub-TLV elements, which includes the first SR sub-TLV element.