Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 587)

unavailable, OSPF 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.
NOTE
For details refer to
Not-so-stubby area (NSSA) on page 587.
• TSA — Similar to a stub area, a TSA does not allow summary routes in addition to not having
external routes.
NOTE
For details refer to
Totally stubby area on page 587.
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 addresses. This aggregate value becomes the
address that is advertised instead all of the individual addresses it represents being advertised. You can
assign up to 32 ranges in an OSPF area.
Totally stubby area
By default, the device sends summary LSAs (LSA Type 3) into stub areas. You can further reduce the
number of link state advertisements (LSA) sent into a stub area by configuring the device to stop
sending summary LSAs (Type 3 LSAs) into the area. This is called assigning a totally stubby area
(TSA). You can disable the summary LSAs when you are configuring the stub area or later after you
have configured the area.
This feature disables origination of summary LSAs, but the device still accepts summary LSAs from
OSPF neighbors and floods them to other neighbors.
When you enter a 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
This feature applies 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 OSPF not-so-stubby area (NSSA) feature enables you to configure OSPF areas that provide the
benefits of stub areas, but that also are capable of importing external route information. OSPF 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 OSPF area. The OSPF specification prohibits summarization of Type 5
LSAs and requires OSPF 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 OSPF network containing an NSSA.
Area range
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