Area Range - Brocade Communications Systems ICX 7250 Series Configuration Manual

When an NSSA contains more than one ABR, OSPFv2 elects one of the ABRs to perform the LSA translation for NSSA.
OSPFv2 elects the ABR with the highest router ID. If the elected ABR becomes unavailable, OSPFv2 automatically elects the
ABR with the next highest router ID to take over translation of LSAs for the NSSA. The election process for NSSA ABRs is
automatic.
• TSA: Similar to a stub area, a TSA does not allow summary routes in addition to not having external routes.

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 (NSSA)
The OSPFv2 not-so-stubby area (NSSA) enables you to configure OSPFv2 areas that provide the benefits of stub areas, but that also
are capable of importing external route information. OSPFv2 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 summarize type 5 External LSAs (external routes) before forwarding them into an
OSPFv2 area. The OSPFv2 specification prohibits summarization of type 5 LSAs and requires OSPFv2 to flood type 5 LSAs
throughout a routing domain. When you configure an NSSA, you can specify a summary-address for aggregating the external routes that
the NSSA's ABR exports into other areas.
The figure below shows an example of an OSPFv2 network containing an NSSA.
Brocade FastIron Layer 3 Routing Configuration Guide
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OSPFv2 areas
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