948 Configuring OSPF and OSPFv3Static Area Range CostThis feature allows a network operator to configure a fixed OSPF cost that isalways advertised when an area range is active. This feature applies to bothOSPFv2 and OSPFv3.An OSPF domain can be divided into areas to limit the processing requiredon each router. Area Border Routers (ABRs) advertise reachability across areaboundaries. It is common to summarize the set of prefixes that an ABRadvertises across an area boundary. RFC 2328 specifies that when an ABRoriginates a type 3 LSA for an active area range, the cost in the LSA is set to“the largest cost of any of the component networks.” Thus, when an area'stopology changes in a way that increases the largest cost, the type 3 LSA mustbe re-originated. In some cases, advertising the change in cost may be lessimportant than preventing the topology change from propagating outside thearea (thus causing routers in other areas to process and flood a changed LSAand rerun their routing table calculations). For this reason, it is common togive the network administrator the option of configuring the cost for an arearange. When a static cost is configured, the cost advertised in the type 3 LSAdoes not depend on the cost of the component networks. Thus, topologychanges within an area do not propagate outside the area, resulting in greaterstability within the OSPF domain.PowerConnect switches also use area ranges to summarize type 7 LSAs whenthey are translated to type 5 LSAs. The cost option may be configured on arearanges used for type 7 to type 5 translation.If an area range is configured for type 3 summarization and the static cost isset to the maximum value, 16,777,215, the range is not advertised. Settingthis static cost is equivalent to configuring a range with the not-advertiseoption. A summary LSA with this metric (LSInfinity) cannot be advertised,according to RFC 2328 section 12.4.3. This behavior is consistent with theindustry standard.If an area range is configured for type 7 to type 5 translation, a type 5 LSA issent if the metric is set to 16,777,215; however, other routers will not computea route from a type 5 LSA with this metric.See "Configuring the Static Area Range Cost" on page 1020 for aconfiguration example.
