| This section covers some of the OSPF
capabilities and associated configurations in more detail. You will
learn how to configure an ABR, how to configure route summarization,
how to use and configure stub/totally stubby areas, and how to use
and configure virtual links.
There are no special commands to make a router an ABR or ASBR.
The router takes on this role by virtue of the areas to which it is
connected. As a reminder, the basic OSPF configuration steps are as
follows:
- Enable OSPF on the
router.
router(config)#router ospf process-id
Identify which IP networks on the router are part of the
OSPF network. For each network, you must identify to which area
the network belongs. When configuring multiple OSPF areas, make
sure to associate the correct network addresses with the desired
area ID.
router(config-router)#network address
wildcard-mask area area-id
(Optional) If the router has at least one interface
connected into a non-OSPF network, perform the proper
configuration steps. At this point the router will be acting as
an ASBR. How the router exchanges (redistributes) non-OSPF route
information with the other OSPF routers is discussed in "Optimizing
Routing Update Operation."
Refer to "Configuring
OSPF in a Single Area," for details about basic OSPF
configuration commands. The main figure shows the configuration commands used to make a
regular and an ABR router.
Note The most common OSPF configuration error is to assign
the network(s) to the wrong area.
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