H3C Technologies H3C SecPath F1000-E - Manual (Page 298)

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LSA is flooded into the local subnet, the Type 10 is flooded into the local area, and the Type 11 is
flooded throughout the whole AS.
Neighbor and Adjacency
In OSPF, the “Neighbor” and ”Adjacency” are two different concepts.
Neighbor: Two routers that have interfaces to a common network. Neighbor relationships are
maintained by, and usually dynamically discovered by, OSPF's hello packets. When a router starts, it
sends a hello packet via the OSPF interface, and the router that receives the hello packet checks
parameters carried in the packet. If parameters of the two routers match, they become neighbors.
Adjacency: A relationship formed between selected neighboring routers for the purpose of exchanging
routing information. Not every pair of neighboring routers become adjacent, which depends on network
types. Only by synchronizing the LSDB via exchanging DD packets and LSAs can two routers become
adjacent.
OSPF Area Partition
Area partition
When a large number of OSPF routers are present on a network, LSDBs may become so large that a
great amount of storage space is occupied and CPU resources are exhausted by performing SPF
computation.
In addition, as the topology of a large network is prone to changes, enormous OSPF packets may be
created, reducing bandwidth utilization. Each topology change makes all routers perform route
calculation.
To solve this problem, OSPF splits an AS into multiple areas, which are identified by area ID. The
boundaries between areas are routers rather than links. A network segment (or a link) can only reside in
one area, in other words, an OSPF interface must be specified to belong to its attached area, as shown
in the figure below.