BigIron RX Series Configuration Guide 689
53-1002253-01
Configuring OSPF
25
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 Brocade implementation of NSSA is based on RFC 3101.
Figure 105 shows an example of an OSPF network containing an NSSA.
FIGURE 105 OSPF network containing an NSSA
This example shows two routing domains, a RIP domain and an OSPF domain. The ASBR inside the
NSSA imports external routes from RIP into the NSSA as Type-7 LSAs, which the ASBR floods
throughout the NSSA.
RIP Domain
NSSA
Area 1.1.1.1
Internal ASBR
OSPF ABR
OSPF Area 0
Backbone
To Next Page
Loading...
