Explanation/Reference:
In a nutshell, the OSPF enhancements for graceful restart are as follows:
- The router attempting a graceful restart originates link-local Opaque-LSAs, herein called Grace-LSAs, announcing its intention to perform a graceful restart within a specified amount of time or "grace period".
- During the grace period, its neighbors continue to announce the restarting router in their LSAs as if it were fully adjacent (i.e., OSPF neighbor state Full), but only if the network topology remains static (i.e., the contents of the LSAs in the link-state database having LS types 1-5,7 remain unchanged and periodic refreshes are allowed).
Reference: https://tools.ietf.org/html/rfc3623