Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 199)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 181
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Configuring OSPF
NOTE
This feature applies only when the Layer 3 Switch 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.
This feature does not apply to Not-So-Stubby Areas (NSSAs).
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: 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 through 18.
The stub cost parameter specifies an additional cost for using a route to or from this area and can
be from 1 through 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.
NOTE
You can assign one area on a router interface. For example, if the system or chassis module has 16
ports, 16 areas are supported on the chassis or module.
Assigning a Not-So-Stubby Area
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 Brocade implementation of NSSA is based on RFC 1587.
Figure 21 shows an example of an OSPF network containing an NSSA.