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IP Routing Features
Configuring OSPF
An OSPF router can be a member of multiple areas. Routers with membership
in multiple areas are known as Area Border Routers (ABRs). Each ABR
maintains a separate topological database for each area the router is in. Each
topological database contains all of the LSA databases for each router within
a given area. The routers within the same area have identical topological
databases. The ABR is responsible for forwarding routing information or
changes between its border areas.
An Autonomous System Boundary Router (ASBR) is a router that is
running multiple protocols and serves as a gateway to routers outside an area
and those operating with different protocols. The ASBR is able to import and
translate different protocol routes into OSPF through a process known as
redistribution. For more details on redistribution and configuration exam-
ples, see
“Enable Route Redistribution” on page 16-49.
Designated Routers in Multi-Access Networks
In a network that has multiple routers attached, OSPF elects one router to
serve as the designated router (DR) and another router on the segment to act
as the backup designated router (BDR). This arrangement minimizes the
amount of repetitive information that is forwarded on the network by
forwarding all messages to the designated router and backup designated
routers responsible for forwarding the updates throughout the network.
Designated Router Election
In a network with no designated router and no backup designated router, the
neighboring router with the highest priority is elected as the DR, and the router
with the next largest priority is elected as the BDR.
If the DR goes off-line, the BDR automatically becomes the DR. The router
with the next highest priority becomes the new BDR.
Not e Priority is a configurable option at the interface level. You can use this
parameter to help bias one Series 5300XL Switch as the DR.
If two neighbors share the same priority, the router with the highest router ID
is designated as the DR. The router with the next highest router ID is desig-
nated as the BDR.
Not e By default, the HP router ID is the lowest numbered IP address configured on
the device. For more information or to change the router ID, see “Changing
the Router ID” on page 16-9.
16-34