Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 194)

176 Brocade ICX 6650 Layer 3 Routing Configuration Guide
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OSPF graceful restart
Dynamic OSPF memory
Brocade ICX 6650 devices dynamically allocate memory for Link State Advertisements (LSAs) and
other OSPF data structures. This eliminates overflow conditions and does not require a reload to
change OSPF memory allocation. So long as the Layer 3 Switch has free (unallocated) dynamic
memory, OSPF can use the memory.
To display the current allocations of dynamic memory, use the show memory command.
OSPF graceful restart
OSPF graceful restart is a high-availability routing feature that minimizes disruption in traffic
forwarding, diminishes route flapping, and provides continuous service during a system restart,
including restart events that occur during a switchover, failover OS upgrade. During such events,
routes remain available between devices.
When OSPF graceful restart is enabled, a restarting router sends special LSAs, called grace LSAs,
to its neighbors either before a planned OSPF restart or immediately after an unplanned restart.
The grace LSAs specify a grace period for neighbors of the restarting router to continue using the
existing routes to and through the router after a restart. When the restarting router comes back up,
it continues to use its existing OSPF routes as if nothing happened. In the background, the router
relearns its neighbors prior to the restart, recalculates its OSPF routes, and replaces existing routes
with new routes as necessary. Once the grace period has passed, adjacent routers resume normal
operation.
OSPF graceful restart is enabled globally by default. In this configuration, all OSPF neighbors are
subject to the graceful restart capability. Neighbor routers must support the helper mode of OSPF
graceful restart, which is enabled by default on all FastIron Layer 3 switches.
NOTE
If a Brocade ICX 6650 device is configured for OSPF graceful restart and is intended to be used in
switchover, the OSPF dead-interval should be changed to 60 seconds on OSPF interfaces to ensure
that the graceful restart process succeeds without a timeout. Instructions for changing the OSPF
dead-interval are provided in
“Modifying interface defaults” on page 184.
The Brocade implementation of OSPF graceful restart supports RFC 3623: Graceful OSPF Restart.
For details on how to configure OSPF graceful restart, refer to “Configuring OSPF graceful restart”
on page 211.