Filter
Top Products
C H A P T E R 13 RIP and OSPF
227
Link-State Database
Upon initialization, each router transmits a link-state advertisement
(LSA) on each of its interfaces. LSAs are collected by each router
and entered into the LSDB of each router. OSPF uses flooding to
distribute LSAs between routers. Any change in routing information
is sent to all of the routers in the network. All routers within an area
have the exact same LSDB. Table 13.1 describes LSA type
numbers.
Areas
OSPF allows parts of a network to be grouped together into areas.
The topology within an area is hidden from the rest of the
autonomous system. Hiding this information enables a significant
reduction in LSA traffic, and reduces the computations needed to
maintain the LSDB. Routing within the area is determined only by the
topology of the area.
The three types of routers defined by OSPF are as follows:
• Internal Router (IR): An internal router has all of its interfaces
within the same area.
Table 13.1: LSA Type Numbers
Type Number Description
1 Router LSA
2 Network LSA
3 Summary LSA
4 AS summary
LSA
5 AS external LSA
7 Not-so-stubby-
area (NSSA)
external LSA