• If helper mode has been disabled through the
graceful-restart helper disable
command, the router drops
the LSA packet.
• If helper mode is enabled, the router enters helper mode if all of the following conditions are met:
• The local router itself is not attempting a graceful restart.
• The local (helping) router has full adjacency with the sending neighbor.
• The value of
lsage
(link state age) in the received LSA is less than the requested grace period.
• The sender of the grace LSA is the same as the originator of the grace LSA.
• Upon entering helper mode, a router performs its helper function for a specific period of time. This time
period is the lifetime value from the router that is in restart mode—minus the value of
lsage
in the received
grace LSA. If the graceful restart succeeds in time, the helper’s timer is stopped before it expires. If the
helper’s timer does expire, the adjacency to the restarting router is brought down, and normal OSPFv3
functionality resumes.
• The dead timer is not honored by the router that is in helper mode.
• A router in helper mode ceases to perform the helper function in any of the following cases:
• The helper router is able to bring up a FULL adjacency with the restarting router.
• The local timer for the helper function expires.
Protocol Shutdown Mode
In this mode the OSPFv3 operation is completely disabled. This is accomplished by flushing self-originated
link state advertisements (LSAs), immediately bringing down local OSPFv3-supported interfaces, and clearing
the Link State Database (LSDB). The non-local LSDB entries are removed by OSPFv3, These are not flooded
(MaxAged).
The protocol shutdown mode can be invoked either manually through the
protocol shutdown
command that
disables the protocol instance or when the OSPFv3 process runs out of memory. These events occur when
protocol shut down is performed:
• The local Router LSA and all local Link LSAs are flushed. All other LSAs are eventually aged out by
other OSPFv3 routers in the domain.
• OSPFv3 neighbors not yet in Full state with the local router are brought down with the Kill_Nbr event.
• After a three second delay, empty Hello packets are immediately sent to each neighbor that has an active
adjacency.
• An empty Hello packet is sent periodically until the dead_interval has elapsed.
• When the dead_interval elapses, Hello packets are no longer sent.
After a Dead Hello interval delay (4 X Hello Interval), the following events are then performed:
• The LSA database from that OSPFv3 instance is cleared.
• All routes from RIB that were installed by OSPFv3 are purged.
The router will not respond to any OSPF control packets it receives from neighbors while in protocol shutdown
state.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
273
Implementing OSPF
Protocol Shutdown Mode