Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 198)

170 Multi-Service IronWare Routing Configuration Guide
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Configuring OSPF
Assign a 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. 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. The device can form adjacencies with other
routers regardless of whether summarization is enabled or disabled for areas on each router.
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 of 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.
To disable summary LSAs for a stub area, enter commands such as the following.
Brocade(config-ospf-router)# area 40 stub 99 no-summary
Syntax: [no] area num | ip-addr stub cost [no-summary]
The num | ip-addr parameter specifies the area number, which can be a number or in IP address
format. If you specify a number, the number can be from 0 – 2,147,483,647.
The stub cost parameter specifies an additional cost for using a route to or from this area and can
be from 1 – 16777215. There is no default. Normal areas do not use the cost parameter.
The no-summary parameter applies only to stub areas and disables summary LSAs from being sent
into the area.
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 2328) 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 NSSA's ABR exports into other areas.
The implementation of NSSA is based on RFC 3101.