IS-IS Node and Adjacency SID

This feature introduces basic support for source packet routing (SPRING) or segment routing for IS-IS.

Segment routing is a control-plane architecture that enables an ingress router to steer a packet through a specific set of nodes and links in the network without relying on the intermediate nodes in the network to determine the actual path it should take. In this context, the term "source" means "the point at which the explicit route is imposed." 

Essentially, segment routing engages IS-IS for advertising the following two types of network segments, or segment IDs (SIDs): 

• Strict forwarded single-hop tunnel that carries packets over a specific link between two nodes, irrespective of the link cost, referred to as adjacency SID. 
• Multihop tunnel using shortest path links between two specific nodes, referred to as node SID. 

Ingress routers can steer a packet through a specified set of nodes and links by prepending the packet with an appropriate combination of node and/or adjacency SIDs.