
Configuring IP Services
9-4
2. The protocol consults an
announce policy
to determine whether or not to
advertise the route to the network.
Note:
The way OSPF applies accept and announce policies to routing
information differs in several ways from the procedure shown in Figure 9-2.
OSPF link-state advertisements (LSAs) are received and placed in the link
state database (LSDB) of the router. The information in the LSDB is also
propagated to other routers in the OSPF routing domain. According to the
OSPF standard, all routers in a given area must maintain a similar database.
To maintain database integrity across the network, a router must not
manipulate received LSAs before propagating them on to other routers. To
accomplish this, OSPF accept and announce policies act in the following
manner:
OSPF accept policies control which OSPF non-self-originated external
routing information is passed to the routing table manager. The accept policies
control only what the local router uses; they do not affect the propagation of
OSPF internal and OSPF non-self-originated external information to other
routers.
OSPF announce policies control which self-originated external routing
updates are placed into the LSDB for distribution according to the OSPF
standard. OSPF announce policies affect what other routers learn but only
with regard to the local router’s self-originated information.
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