
IP Concepts, Terminology, and Features
117356-A Rev. A 1-17
Periodically, the routing table manager announces routes to other routers in the
network:
1. The routing table manager forwards a route for advertisement to the protocol.
2. The protocol consults an announce policy to determine whether or not to
advertise the route to the network.
IP accept and announce policies and policy parameters are described in
A
ppendix B.
IP import and export filters and filter parameters are described in A
ppendix C.
Note: The way OSPF applies accept and announce policies to routing
information differs in several ways from the procedure shown in Figure 1-4.
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 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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