Helper Mode; Protocol Shutdown Mode - Cisco ASR 9000 Series Configuration Manual

Graceful Shutdown for OSPFv3
The following are general details about restart mode. More detailed information on behavior and certain
restrictions and requirements appears in
• If OSPFv3 attempts a restart too soon after the most recent restart, the OSPFv3 process is most likely
crashing repeatedly, so the new graceful restart stops running. To control the period between allowable
graceful restarts, use the graceful-restart interval command.
• When OSFPv3 starts a graceful restart with the first interface that comes up, a timer starts running to
limit the duration (or lifetime) of the graceful restart. You can configure this period with the
graceful-restart lifetime command. On each interface that comes up, a grace LSA (Type 11) is flooded
to indicate to the neighboring routers that this router is attempting graceful restart. The neighbors enter
into helper mode.
• The designated router and backup designated router check of the hello packet received from the restarting
neighbor is bypassed, because it might not be valid.

Helper Mode

Helper mode is enabled by default. When a (helper) router receives a grace LSA (Type 11) from a router that
is attempting a graceful restart, the following events occur:
• 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:
• 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:

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).
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
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◦ 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.
◦ The helper router is able to bring up a FULL adjacency with the restarting router.
◦ The local timer for the helper function expires.
Graceful Restart Requirements and Restrictions, on page 351
Implementing OSPF
section.
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