Using and processing per slice segment identifiers in a network employing segment routing

1. A computer-implemented method for configuring and/or using the same prefix segment identifier (SID) provided for either (A) more than one prefix within an interior gateway protocol (IGP) domain, or (B) one prefix with more than one path computation algorithm within the IGP domain, the computer-implemented method comprising:

a) receiving, by a node in the IGP domain, an IGP advertisement including both (1) a prefix SID and (2) a segment routing global block (SRGB) slice identifier;

b) determining whether or not the SRGB slice identified by the SRGB slice identifier is provisioned on the node; and

c) responsive to a determination that the SRGB slice identified by the SRGB slice identifier is not provisioned on the node, not processing the prefix SID included in the received IGP advertisement, and otherwise

responsive to a determination that the SRGB slice identified by the SRGB slice identifier is provisioned on the node,

1) processing the prefix SID and SRGB slice to generate a unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided, and

2) updating a label forwarding information base (LFIB) for the node using the unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided and the one or more prefix for which the prefix SID is provided.

2. The computer implemented method of claim 1 wherein the act of processing the prefix SID and SRGB slice to generate a unique, per SRGB slice, label for the prefix includes adding the prefix SID, as an index value, to a base defined by the SRGB slice.

3. The computer implemented method of claim 1 wherein the act of processing the prefix SID and SRGB slice to generate a unique, per SRGB slice, label for the prefix includes subtracting the prefix SID, as an index value, from a maximum value defined by the SRGB slice.

4. The computer-implemented method of claim 1 wherein the LFIB for the node includes an entry with the unique, per SRGB slice, label for the prefix and the prefix, the computer-implemented method further comprising:

d) receiving a packet including the prefix;

e) using the prefix to look up the unique, per SRGB slice, label in the LFIB; and

f) forwarding the packet using the unique, per SRGB slice, label.

5. The computer-implemented method of claim 1 , wherein the router belongs to a specific slice of an SR domain within the IGP domain.

6. The computer-implemented method of claim 1 , wherein the router belongs to at least two specific slices of an SR domain within the IGP.

7. The computer-implemented method of claim 1 , wherein the same prefix SID is provided for more than one prefix within the IGP domain.

8. The computer-implemented method of claim 1 , wherein the same prefix SID is provided for one prefix with more than one path computation algorithm within the IGP domain.

9. The computer-implemented method of claim 1 , wherein the IGP advertisement is a prefix SID sub-TLV carried in a Network Layer Reachability Information (NLRI) field and including both (1) the prefix SID and the segment routing global block (SRGB) slice identifier.

10. The computer-implemented method of claim 1 , wherein the SRGB slice corresponds to a ring.

11. A network device for configuring and/or using the same prefix segment identifier (SID) provided for either (A) more than one prefix within an interior gateway protocol (IGP) domain, or (B) one prefix with more than one path computation algorithm within the IGP domain, the device comprising:

a) an interface;

b) at least one processor; and

c) a storage device storing processor-executable instructions which, when executed by the at least one processor, cause the at least one processor to perform a method responsive to receiving, by the interface, an IGP advertisement including both ( 1 ) a prefix SID and (2) a segment routing global block (SRGB) slice identifier, the method including

1) determining whether or not the SRGB slice identified by the SRGB slice identifier is provisioned on the network device, and 2) responsive to a determination that the SRGB slice identified by the SRGB slice identifier is not provisioned on the network device, not processing the prefix SID included in the received IGP advertisement, and otherwise

responsive to a determination that the SRGB slice identified by the SRGB slice identifier is provisioned on the network device,

processing the prefix SID and SRGB slice to generate a unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided, and

updating a label forwarding information base (LFIB) for the node using the unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided and the one or more prefix for which the prefix SID is provided.

12. A non-transitory computer-readable medium storing computer-executable instructions which, when executed by at least one computer, cause the computer to perform a computer-implemented method for configuring and/or using the same prefix segment identifier (SID) provided for either (A) more than one prefix within an interior gateway protocol (IGP) domain, or (B) one prefix with more than one path computation algorithm within the IGP domain, the computer-implemented method including

a) receiving, by a node in the IGP domain, an IGP advertisement including both (1) a prefix SID and (2) a segment routing global block (SRGB) slice identifier, b) determining whether or not the SRGB slice identified by the SRGB slice identifier is provisioned on the node, and c) responsive to a determination that the SRGB slice identified by the SRGB slice identifier is not provisioned on the node, not processing the prefix SID included in the received IGP advertisement, and otherwise

responsive to a determination that the SRGB slice identified by the SRGB slice identifier is provisioned on the node,

1) processing the prefix SID and SRGB slice to generate a unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided,

2) updating a label forwarding information base (LFIB) for the node using the unique, per SRGB slice, MPLS label for each of the one or more prefix for which the prefix SID is provided and the one or more prefix for which the prefix SID is provided.