Dell PowerConnect FCS624S Configuration Guide - Page 977

Configuring OSPF 29 The stub 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 (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 Dell implementation of NSSA is based on RFC 1587. Figure 142 shows an example of an OSPF network containing an NSSA. FIGURE 142 OSPF network containing an NSSA RIP Domain Layer 3 Switch Layer 3 Switch NSSA Area 1.1.1.1 Internal ASBR Layer 3 Switch OSPF Area 0 Backbone OSPF ABR 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. PowerConnect B-Series FCX Configuration Guide 935 53-1002266-01