SMC Networks 8926EM, Management Manual

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Configuring the Open Shortest Path First Protocol
20-21
20
Command Usage
• Before you create the backbone, a stub or NSSA, first specify the address range
for the area using the Network Area Address Configuration screen (page 20-31).
• Stubs and NSSAs cannot be used as a transit area, and should therefore be placed
at the edge of the routing domain.
• A stub or NSSA can have multiple ABRs or exit points. However, all of the exit
points and local routers must contain the same external routing data so that the exit
point does not need to be determined for each external destination.
Command Attributes
• Area ID – Identifier for an normal area, stub or NSSA. The area ID must be in the
form of an IPv4 address.
• Area Type – Specifies a normal area, stub area, or not-so-stubby area (NSSA).
Area ID 0.0.0.0 is set to the backbone by default. (Default: Normal area)
• Default Cost – Cost for the default summary route sent into a stub from an area
border router (ABR). (Range: 0-16777215; Default: 1)
- Note that if you set the default cost to “0,” the router will not advertise a default
route into the attached stub.
• Summary – Makes an ABR send a Type-3 summary link advertisement into a stub.
(Default: Summary)
A stub is designed to save routing table space by blocking Type-4 AS summary
LSAs and Type 5 external LSAs. If you use the “NoSummary” option to also block
Type-3 summary LSAs that advertise the default route for destinations external to
the local area or the AS, the stub will become completely isolated.
Define an area as a totally stubby area only if routers in the area do not require
summary LSAs from other areas.
Note:
This router supports up to 16 total areas (either normal transit areas, stubs, or
NSSAs).