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The following are four different types of OSPF routers
that exist:

- Internal router
– As discussed
previously, routers that have all their interfaces within the same
area are called internal routers. Internal routers in the same area
have identical link-state databases and run a single copy of the
routing algorithm.
- Backbone router
– Routers that
are attached to the backbone area of the OSPF network are called
backbone routers. They have at least one interface connected to Area
0, the backbone area. These routers maintain OSPF routing
information using the same procedures and algorithms as internal
routers.
- Area Border Router (ABR)
–
ABRs are routers with interfaces attached to multiple areas. They
maintain separate link-state databases for each area to which they
are connected, and they route traffic destined to or arriving from
other areas. ABRs are exit points for the area, which means that
routing information destined for another area can travel there only
by way of the of the local area ABR. ABRs summarize information
about the attached areas from their link-state databases and
distribute the information into the backbone. The backbone ABRs then
forward the information to all other connected areas. An area can
have one or more ABRs.
- Autonomous System Boundary Router
(ASBR)
– ASBRs are routers that have at least one interface
connected to an external internetwork, another autonomous system,
such as a non-OSPF network. These routers can import non-OSPF
network information to the OSPF network, and OSPF to non-OSPF. This
is referred to as redistribution.
A router can be more than one router
type. For example, if a router interconnects to Area 0 and Area 1, as
well as to a non-OSPF network, it would be both an ABR and an ASBR.
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Interactive Media Activity
Drag and Drop: OSPF Router Types
Upon completion of this activity, the student will be able to
identify the four different types of OSPF routers.

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