Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 322)

Assign a 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 (RFC 2740) 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 an address range for aggregating the external routes
that the NSSAs ABR exports into other areas.
Since the NSSA is partially "stubby" the ABR does not flood external LSAs from the backbone into the
NSSA. To provide access to the rest of the Autonomous System (AS), the ABR generates a default
Type-7 LSA into the NSSA.
Configuring an NSSA
Using the area nssa command, you can block the generation of type-3 and type-7 LSAs into an
NSSA. This command also provides an option to configure the NSSA translator role.
Configuration examples
The following example creates an NSSA area with an area-id 100. If the router is an ABR then a
type-3 summary LSA will be originated into the NSSA area and if the router is an ASBR then type-7
NSSA external LSA will be generated into NSSA area with a default external metric value of 10. The
routers NSSA translator role will be set to candidate and it will participate in NSSA translation election.
device(config-ospf6-router)# area 100 nssa
The following example modifies the NSSA area 100 wherein type-7 NSSA external LSA will not be
originated into NSSA area. But the type-3 summary LSAs will still be originated into NSSA area.
device(config-ospf6-router)# area 100 nssa no-redistribution
The following example modifies the NSSA area 100 wherein origination of type-3 summary LSAs
(apart from type-3 default summary) will be blocked into NSSA area. The CLI works in incremental
fashion and the origination of type-7 LSA will be continued to be blocked as 'no-redistribution' option
was enabled in the previous command.
device(config-ospf6-router)#area 100 nssa no-summary
The following example modifies the NSSA area 100 wherein origination of the self-router acts as
NSSA translator. The generation of type-3 & type-7 LSA will still be blocked into NSSA area.
device(config-ospf6-router)#area 100 nssa translator-always
The following example modifies the NSSA area 100 wherein origination of type-3 summary will be
allowed, but origination of type-7 LSA will still be blocked. Also the self-router will still act as NSSA
translator-always.
device(config-ospf6-router)#no area 100 nssa no-summary
Although the NSSA configuration can be done in an incremental fashion during show-run, all the
configuration options will be displayed in just one line. For example, the output of the show run would
be:
device(config-ospf6-router)#area 100 nssa no-redistribution translator-always
Assign a Not-So-Stubby Area (NSSA)
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