C
HAPTER
20
| Unicast Routing
Configuring the Open Shortest Path First Protocol (Version 2)
– 515 –
◆ Redistribute – Disable this option when the router is an NSSA Area
Border Router (ABR) and routes only need to be imported into normal
areas (see "Redistributing External Routes" on page 521), but not into
the NSSA. In other words, redistribution should be disabled to prevent
the NSSA ABR from advertising external routing information (learned
through routers in other areas) into the NSSA. (Default: Enabled)
◆ Originate Default Information – When the router is an NSSA Area
Border Router (ABR) or an NSSA Autonomous System Boundary Router
(ASBR), this option causes it to generate a Type-7 default LSA into the
NSSA. This default provides a route to other areas within the AS for an
NSSA ABR, or to areas outside the AS for an NSSA ASBR.
(Default: Disabled)
An NSSA is similar to a stub, because when the router is an ABR, it can
send a default route for other areas in the AS into the NSSA using the
Originate Default Information option. However, an NSSA is different
from a stub, because when the router is an ASBR, it can import a
default external AS route (for routing protocol domains adjacent to the
NSSA but not within the OSPF AS) into the NSSA using this option.
◆ Metric Type – Type 1 or Type 2 external routes. When using Type 2,
routers do not add internal cost to the external route metric.
(Default: Type 2)
◆ Metric – Metric assigned to Type-7 default LSAs. (Range: 1-16777214;
Default: 1)
◆ Default Cost – Cost for the default summary route sent into an NSSA
from an area border router (ABR). (Range: 0-16777215; Default: 0)
Note that whe the default cost is set to “0,” the router will not advertise
a default route into the attached NSSA.
◆
Summary
–
Controls the use of summary routes. (Default: Summary)
■
Summary
–
Unlike stub areas, all Type-3 summary LSAs will be
imported into NSSAs to ensure that internal routes are always
chosen over Type-7 NSSA external routes.
■
No Summary
–
Allows an area to retain standard NSSA features,
but does not inject inter-area routes (Type-3 and Type-4 summary
routes) into this area. Instead, it advertises a default route as a
Type-3 LSA.
WEB INTERFACE
To configure protocol settings for an NSSA:
1. Click Routing Protocol, OSPF, Area.
2. Select Configure Area from the Step list.
3. Select Configure NSSA Area from the Action list.
4. Select a Process ID, and modify the routing behavior for an NSSA.
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