What happens when a segment-routing TE tunnel loses the link and there is no secondary path in place?

The headend router does not automatically generate a new path based on bandwidth in this scenario; instead, it typically relies on pre-provisioned paths or the controller to recalculate and establish a new path, and the invalidation timer is for tearing down the failed path.

The tail-end router might send alerts, but the primary action regarding the tunnel's state, especially bringing it down due to a failed link, is handled by the headend router.

Upon detecting a link failure for a Segment Routing TE tunnel, the headend router starts an invalidation timer. If no other valid path can be found or established within this timer's duration, the tunnel is brought down, signifying its failure.

Revalidating SID hops is part of path computation or verification, but in the event of a link loss without a secondary path, the immediate action is to detect the failure and manage the tunnel's state, often leading to invalidation.