Ospf Neighbors - Avaya 8800 Configuration Manual

OSPF and RIP fundamentals
• The interface priority on R5 is 0; therefore, R5 cannot become a designated router
(DR).
• Configure the OSPF router priority so that R1 becomes the DR (priority 100) and R2
becomes the backup designated router (BDR) with a priority value (priority 50).
Use stub or NSSA areas to reduce the LSDB size by excluding external LSAs. The stub ABR
advertises a default route into the stub area for all external routes.

OSPF neighbors

In an OSPF network, any two routers that have an interface to the same network are neighbors.
Routers use the Hello Protocol to discover their neighbors and to maintain neighbor
relationships. On a broadcast or point-to-point network, the Hello Protocol dynamically
discovers neighbors. On an NBMA network, you must manually configure neighbors for the
network.
The Hello Protocol provides bidirectional communication between neighbors. Periodically,
OSPF routers send Hello packets over all interfaces. Included in these Hello packets is the
following information:
• router priority
• router Hello Timer and Dead Timer values
• list of routers that sent the router Hello packet on this interface
• router choice for designated router (DR) and backup designated router (BDR)
Bidirectional communication is determined when one router discovers itself listed in its
neighbor Hello packet.
NBMA interfaces whose router priority is a positive, nonzero value are eligible to become DRs
for the NBMA network and are configured with a list of all attached routers. The neighbors list
includes each neighbor IP address and router priority. In an NBMA network, any router with a
priority other than zero is eligible to become the DR for the NBMA network. You must manually
configure the IP address, mask, and router priority of neighbors on routers that are eligible to
become the DR or BDR for the network.
Logging messages indicate when an OSPF neighbor state change occurs. Each log message
indicates the previous state and the new state of the OSPF neighbor. The log message
generated for system traps also indicates the previous state and the current state of the OSPF
neighbor.
Neighbors can form an adjacency to exchange routing information. When two routers form an
adjacency, they perform a database exchange process to synchronize their topological
databases. When their databases are synchronized, the routers are said to be fully adjacent.
Bandwidth is conserved because, from this point, only routing change information is passed
between the adjacent routers.
40 Configuration — OSPF and RIP June 2011