Seamless bidirectional forwarding detection discriminator based return path determination

1. A method comprising:

assigning, at a first network element, a first discriminator associated with a first discriminator identifier;

assigning, at the first network element, a second discriminator associated with a second discriminator identifier, wherein the second discriminator is different from the first discriminator;

receiving, at the first network element, a seamless bidirectional forwarding detection (S-BFD) control packet sent from a second network element, the S-BFD control packet including one of the first discriminator identifier or the second discriminator identifier;

determining whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

initiating an S-BFD reflector session to transmit a response S-BFD control packet to the second network element along a return path determined based on whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

when the first discriminator identifier is included in the S-BFD control packet, determining the return path for the response S-BFD control packet by the first network element; and

when the second discriminator identifier is included in the S-BFD control packet, determining the return path for the response S-BFD control packet specified by the second network element in the S-BFD control packet.

2. The method of claim 1 , wherein the return path determined by the first network element is a shortest path to the second network element.

3. The method of claim 1 , wherein the return path specified by the second network element comprises a segment list included in a segment routing header of the S-BFD control packet.

4. The method of claim 1 , further comprising:

receiving, at the first network element, a plurality of S-BFD control packets sent from the second network element;

wherein a first S-BFD control packet includes the second discriminator identifier and a first segment list in a segment routing header of the first S-BFD control packet, the first segment list specifying a first return path for a response S-BFD control packet transmitted from the first network element to the second network element; and

wherein a second S-BFD control packet includes the second discriminator identifier and a second segment list in a segment routing header of the second S-BFD control packet, the second segment list specifying a second return path for a response S-BFD control packet transmitted from the first network element to the second network element, wherein the second return path is different than the first return path.

5. The method of claim 1 , wherein the first network element and the second network element are disposed in a network comprising a plurality of network elements; and

wherein the second network element includes one of the first discriminator identifier or the second discriminator identifier in the S-BFD control packet based on network topology information received by the second network element from one or more of the plurality of network elements.

6. The method of claim 5 , wherein the second network element determines information for specifying the return path included in the S-BFD control packet based on the received network topology information.

7. The method of claim 1 , wherein the S-BFD control packet is one of:

an internet protocol version 4 (IPv4) packet;

an internet protocol version 6 (IPv6) packet; and

a Multiprotocol Label Switching (MPLS) packet.

8. One or more non-transitory computer readable storage media encoded with instructions that, when executed by a processor of a first network element, cause the processor to:

assign, at the first network element, a first discriminator associated with a first discriminator identifier;

assign, at the first network element, a second discriminator associated with a second discriminator identifier, wherein the second discriminator is different from the first discriminator;

receive, at the first network element, a seamless bidirectional forwarding detection (S-BFD) control packet sent from a second network element, the S-BFD control packet including one of the first discriminator identifier or the second discriminator identifier;

determine whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

initiate an S-BFD reflector session to transmit a response S-BFD control packet to the second network element along a return path determined based on whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

when the first discriminator identifier is included in the S-BFD control packet, determine the return path for the response S-BFD control packet by the first network element; and

when the second discriminator identifier is included in the S-BFD control packet, determine the return path for the response S-BFD control packet specified by the second network element in the S-BFD control packet.

9. The one or more non-transitory computer readable storage media of claim 8 , wherein the return path determined by the first network element is a shortest path to the second network element.

10. The one or more non-transitory computer readable storage media of claim 8 , wherein the return path specified by the second network element comprises a segment list included in a segment routing header of the S-BFD control packet.

11. The one or more non-transitory computer readable storage media of claim 8 , further comprising instructions that cause the processor to:

receive, at the first network element, a plurality of S-BFD control packets sent from the second network element;

wherein a first S-BFD control packet includes the second discriminator identifier and a first segment list in a segment routing header of the first S-BFD control packet, the first segment list specifying a first return path for a response S-BFD control packet transmitted from the first network element to the second network element; and

wherein a second S-BFD control packet includes the second discriminator identifier and a second segment list in a segment routing header of the second S-BFD control packet, the second segment list specifying a second return path for a response S-BFD control packet transmitted from the first network element to the second network element, wherein the second return path is different than the first return path.

12. The one or more non-transitory computer readable storage media of claim 8 , wherein the first network element and the second network element are disposed in a network comprising a plurality of network elements; and

further comprising instructions that, when executed by a processor of the second network element, cause the processor to:

receive, at the second network element, network topology information from one or more of the plurality of network elements; and

include one of the first discriminator identifier or the second discriminator identifier in the S-BFD control packet based on the received network topology information.

13. The one or more non-transitory computer readable storage media of claim 12 , further comprising instructions that cause the processor of the second network element to:

determine information for specifying the return path included in the S-BFD control packet based on the received network topology information.

14. The one or more non-transitory computer readable storage media of claim 8 , wherein the S-BFD control packet is one of:

an internet protocol version 4 (IPv4) packet;

an internet protocol version 6 (IPv6) packet; and

a Multiprotocol Label Switching (MPLS) packet.

15. An apparatus comprising:

a plurality of network ports configured to receive inbound packets and to send outbound packets;

a memory;

a processor coupled to the memory and to the plurality of network ports, wherein the processor is configured to:

assign a first discriminator associated with a first discriminator identifier;

assign a second discriminator associated with a second discriminator identifier, wherein the second discriminator is different from the first discriminator;

receive a seamless bidirectional forwarding detection (S-BFD) control packet sent from a network element, the S-BFD control packet including one of the first discriminator identifier or the second discriminator identifier;

determine whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

initiate an S-BFD reflector session to transmit a response S-BFD control packet to the network element along a return path determined based on whether the first discriminator identifier or the second discriminator identifier is included in the S-BFD control packet;

when the first discriminator identifier is included in the S-BFD control packet, determine the return path for the response S-BFD control packet by the apparatus; and

when the second discriminator identifier is included in the S-BFD control packet, determine the return path for the response S-BFD control packet specified by the network element in the S-BFD control packet.

16. The apparatus of claim 15 , wherein the return path determined by the apparatus is a shortest path to the network element.

17. The apparatus of claim 15 , wherein the return path specified by the network element comprises a segment list included in a segment routing header of the S-BFD control packet.

18. The apparatus of claim 15 , wherein the processor is further configured to:

receive a plurality of S-BFD control packets sent from the network element;

wherein a first S-BFD control packet includes the second discriminator identifier and a first segment list in a segment routing header of the first S-BFD control packet, the first segment list specifying a first return path for a response S-BFD control packet transmitted from the apparatus to the network element; and

wherein a second S-BFD control packet includes the second discriminator identifier and a second segment list in a segment routing header of the second S-BFD control packet, the second segment list specifying a second return path for a response S-BFD control packet transmitted from the apparatus to the network element, wherein the second return path is different than the first return path.

19. The apparatus of claim 18 , wherein the first segment list comprises a first ordered set of a plurality of segment identifiers for one or more network elements of a plurality of network elements;

wherein the second segment list comprises a second ordered set of a plurality of segment identifiers for one or more network elements of the plurality of network elements; and

wherein at least one segment identifier in the first ordered set is different from the plurality of segment identifiers in the second ordered set.

20. The apparatus of claim 15 , wherein the S-BFD control packet is one of:

an internet protocol version 4 (IPv4) packet;

an internet protocol version 6 (IPv6) packet; and

a Multiprotocol Label Switching (MPLS) packet.