The subnet space is 64 bits long. Collisions between pseudo-random values only become likely when you have billions of nodes, so it's not worth the effort to p

The subnet space is 64 bits long. Collisions between pseudo-random values only become likely when you have billions of nodes, so it's not worth the effort to preemptively avoid them. This would also require all nodes to implement the same algorithm, which means it's not incrementally deployable. Edit: The actual RFC7217 algorithm contains a DAD_Counter field in the hash input. In the event of a collision, the counter increments, generating a new address.