Restarting and Helper Mode
Routers involved with graceful restart fill one of two roles: the restarting router or the helper router.
With graceful restart, the router that is restarting sends out Grace-LSAs informing its neighbors that it is in graceful restart mode, how long the helper router should assist with the restart (the grace period), and why the restart occurred. If the neighboring routers are configured to help with the graceful restart (helper-mode), they will continue to advertise the restarting router as if it was fully adjacent. Traffic continues to be routed as though the restarting router is fully functional. If the network topology changes, the helper routers will stop advertising the restarting router. The helper router will continue in helper mode until the restarting router indicates successful termination of graceful restart, the Grace‑LSAs expire, or the network topology changes. A router can be configured for graceful restart, and for helper-mode separately. A router can be a helper when its neighbor restarts, and can in turn be helped by a neighbor if it restarts.