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Preliminary November 23, 1998
MultiVoice Gateway for the MAX— User’s Guide
Configuring OSPF Routing
Introduction to OSPF
Exchange of routing information
OSPF uses a topological database of the network and propagates only changes to the database.
Part of the SPF algorithm involves acquiring neighbors, then forming an adjacency with one
neighbor, as shown in Figure 9-2.
Figure 9-2. Adjacency between neighboring routers
An OSPF router dynamically detects its neighboring routers by sending its Hello packets to the
multicast address
All SPFRouters
. It then attempts to form adjacencies with some of its
newly acquired neighbors.
Adjacency is a relationship formed between selected neighboring routers for the purpose of
exchanging routing information. Not every pair of neighboring routers becomes adjacent.
Adjacencies are established during network initialization in pairs, between two neighbors. As
the adjacency is established, the neighbors exchange databases and build a consistent,
synchronized database between them.
When an OSPF router detects a change on one of its interfaces, it modifies its topological
database and multicasts the change to its adjacent neighbor, which in turn propagates the
change to its adjacent neighbor until all routers within an area have synchronized topological
databases. This results in quick convergence among routers. OSPF routes can also be
summarized in link-state advertisements (LSAs).
Designated and backup designated routers
In OSPF terminology, a broadcast network is any network that has more than two OSPF
routers attached and that supports the capability to address a single physical message to all of
the attached routers.
Figure 9-3. Designated and backup designated routers
The MultiVoice Gateway can function as a designated router (DR) or backup designated router
(BDR). However, many sites choose to assign a LAN-based router for these roles in order to
