Brocade Communications Systems ICX 7250 series, Руководство по настройке

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Area range
You can further consolidate routes at an area boundary by defining an area range. The area range allows you to assign an aggregate
value to a range of IP and IPv6 addresses.
This aggregate value becomes the address that is advertised instead of all the individual addresses it represents being advertised. You
have the option of adding the cost to the summarized route. If you do not specify a value, the cost value is the default range metric
calculation for the generated summary LSA cost. You can temporarily pause route summarization from the area by suppressing the type
3 LSA so that the component networks remain hidden from other networks.
You can assign up to 32 ranges in an OSPF area.
Stub area and totally stubby area
A stub area is an area in which advertisements of external routes are not allowed, reducing the size of the database. A totally stubby area
(TSA) is a stub area in which summary link-state advertisement (type 3 LSAs) are not sent.
A stub area disables advertisements of external routes. By default, the ABR sends summary LSAs (type 3 LSAs) into stub areas. You can
further reduce the number of LSAs sent into a stub area by configuring the device to stop sending type 3 LSAs into the area. You can
disable the summary LSAs to create a TSA when you are configuring the stub area or after you have configured the area.
The stub area disables origination of summary LSAs, but the device still accepts summary LSAs from OSPF neighbors and floods them
to other neighbors.
When you enter the area stub no-summary command to disable the summary LSAs, the change takes effect immediately. If you apply
the option to a previously configured area, the device flushes all the summary LSAs it has generated (as an ABR) from the area.
NOTE
Stub areas and TSAs apply only when the device is configured as an Area Border Router (ABR) for the area. To completely
prevent summary LSAs from being sent to the area, disable the summary LSAs on each OSPF router that is an ABR for the
area.
Not-so-stubby area
A not-so-stubby-area (NSSA) is an OSPFv3 area that provides the benefits of stub areas with the extra capability of importing external
route information. OSPFv3 does not flood external routes from other areas into an NSSA, but does translate and flood route information
from the NSSA into other areas such as the backbone.
NSSAs are especially useful when you want to advertise type 5 External LSAs (external routes) before forwarding them into an OSPFv3
area. When you configure an NSSA, you can specify an address range for aggregating the external routes that the ABR of the NSSAs
exports into other areas.
The OSPFv3 specification (RFC 2740) prohibits the advertising of type 5 LSAs and requires OSPFv3 to flood type 5 LSAs throughout
a routing domain.
You can block the generation of type 3 and type 7 LSAs into an NSSA. You can also configure the NSSA translator role. If the router is
an ABR, a type 3 summary LSA is originated into the NSSA. If the router is an ASBR, a type 7 NSSA External LSA is generated into the
NSSA with a default external metric value of 10. The device's NSSA translator role is set to candidate and the router participates in NSSA
translation election.
In the case where an ASBR should generate type 5 LSAs into normal areas and should not generate type 7 LSAs into an NSSA, you can
prevent an NSSA ABR from generating type 7 LSAs into an NSSA.
OSPFv3 areas
Brocade FastIron Layer 3 Routing Configuration Guide
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