Which role does the Adjacency-SID sub-TLV extension perform in the IS-IS routing protocol?
Correct Answer: D
A new IS-IS sub-TLV is defined: the Adjacency Segment Identifier (Adj-SID) sub-TLV.
The Adj-SID sub-TLV is an optional sub-TLV carrying the Segment Routing IGP-Adjacency-SID as defined in [RFC8402] with flags and fields that may be used, in future extensions of Segment Routing, for carrying other types of SIDs.
IS-IS adjacencies are advertised using one of the IS Neighbor TLVs below:
TLV-22 (Extended IS reachability) [RFC5305]
TLV-222 (MT-ISN) [RFC5120]
TLV-23 (IS Neighbor Attribute) [RFC5311]
TLV-223 (MT IS Neighbor Attribute) [RFC5311]
TLV-141 (inter-AS reachability information) [RFC5316]
Multiple Adj-SID sub-TLVs MAY be associated with a single IS Neighbor.