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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 137
configured between two border routers that both have a
connection to their respective area 0s.
Neighbors
Routers that are connected to the same area or segment
become neighbors in that area. Neighbors are elected via the
Hello protocol. IP multicast is used to send out Hello packets
to other routers on the segment. Routers become neighbors
when they see themselves listed in a Hello packet sent by
another router on the same segment. In this way, two-way
communication is guaranteed to be possible between any two
neighbor routers.
Any two routers must meet the following conditions before the
become neighbors:
• Area ID − two routers having a common segment
− their interfaces have to belong to the same
area on that segment. Of course, the interfaces
should belong to the same subnet and have the
same subnet mask.
• Authentication − OSPF allows for the
configuration of a password for a specific area.
Two routers on the same segment and belonging
to the same area must also have the same OSPF
password before they can become neighbors.
• Hello and Dead Intervals − The Hello interval
specifies the length of time, in seconds, between
the hello packets that a router sends on an
OSPF interface. The dead interval is the number
of seconds that a router’s Hello packets have not
been seen before its neighbors declare the OSPF
router down. OSPF routers exchange Hello
packets on each segment in order to
acknowledge each other’s existence on a