D-Link DFL-1600 User Manual page 95

10.3. Routing Algorithms
configured to connect to the backbone through a non-backbone area. VLink
can also be used to link through partitioned backbone areas.
A normal OSPF area acts like a private network connecting to the
backbone area via some router called
ABRs have interfaces in more than one area, and maintains separate
routing information databases for each area to which they are connecting
by an interface. The routers reside in the same OSPF area only need to
learn and synchronize link-state information with the ABR.
Some Routers that exchange routing information with routers in other ASs
are called
ASBRs introduce externally learned routes to the AS and flood the external
routing advertisement throughout all OSPF normal areas.
To reduce the flooding traffic of external routes advertisement, a special
area called
configured, the ABR will automatically advertise a default route so that
routers in the stub area can reach destinations outside the area. The
default route becomes the single exit point of the stub area, and the area
will not accept broadcasts of external routes.
Operating Process
Establishment – "Hello"
At the initialization stage, each router within an area detects its
directly connected network, and sends "Hello" packets to all its OSPF
enabled interfaces to determine who their neighboring routers are.
Routers having interfaces directly connected and residing in the same
OSPF area become neighbors.
When a router sends and receives "Hello" packets and detects
multiple routers in an AS, it will select a
and also a
link-state information exchange.
DR and BDR are automatically elected by "Hello" protocol on every
OSPF broadcast network. The
configurable on a per-interface basis is the parameter that controls
the election. The router with the highest priority number becomes
can be configured. When a stub area is
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for further
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