??Type router that is restarting. Each time
??Type 9 or Intra–Area Prefix LSA:
This LSA is flooded by every router. When the state of links change, the
update is sent in intra–area prefix LSA to a local area. Intra–area prefix
LSA does not cause the re–computation of the SPF algorithm.
Type 11 or
Grace LSAs: Grace LSAs
are used for a graceful restart of OSPFv3. These LSAs are sent by a router
that is restarting. Each time the router is restarting, it sends this LSA
using a link–local flooding scope (Cisco.com. 2016).
Flooding and LSA Group Pacing
OSPFv3 floods LSAs to
different segments of a network, depending on the LSA type. The protocol uses
three different flooding scopes namely:
Link–local where LSAs are flooded only on links that
are directly attached to the router’s interface. This flooding scope is
used to send Link LSA and Grace LSA.
Area–local where LSAs are only flooded within a single
OSPF area. LSA types 1, 2, 3, 4, and 9 are flooded using this flooding
AS scope where LSAs are only flooded within a single
routing domain. This flooding scope is used for sending AS External LSAs
Using OSPF flooding scope
guarantees that routing information for all routers remains identical throughout
the network. LSAs are flooded depending on the configuration of the OSPFv3
area. The LSAs are sent based on a link–state refresh time. By default,
link–state refresh time is every 30 minutes even though all LSAs do not have
the same link–state refresh time.
rate at which LSAs are flooded in the network can be controlled by using LSA
group pacing feature of OSPF. Using OSPF LSA group pacing ensures that high
router CPU utilization is greatly reduced. Group pacing feature allows OSPFv3
to combine multiple LSAs with identical link–state refresh time into a single
routing update instead of flooding them separately.