Dell PowerConnect 8100 User's Configuration Guide - Page 948

Static Area Range Cost This feature allows a network operator to configure a fixed OSPF cost that is always advertised when an area range is active. This feature applies to both OSPFv2 and OSPFv3. An OSPF domain can be divided into areas to limit the processing required on each router. Area Border Routers (ABRs) advertise reachability across area boundaries. It is common to summarize the set of prefixes that an ABR advertises across an area boundary. RFC 2328 specifies that when an ABR originates 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's topology changes in a way that increases the largest cost, the type 3 LSA must be re-originated. In some cases, advertising the change in cost may be less important than preventing the topology change from propagating outside the area (thus causing routers in other areas to process and flood a changed LSA and rerun their routing table calculations). For this reason, it is common to give the network administrator the option of configuring the cost for an area range. When a static cost is configured, the cost advertised in the type 3 LSA does not depend on the cost of the component networks. Thus, topology changes within an area do not propagate outside the area, resulting in greater stability within the OSPF domain. PowerConnect switches also use area ranges to summarize type 7 LSAs when they are translated to type 5 LSAs. The cost option may be configured on area ranges used for type 7 to type 5 translation. If an area range is configured for type 3 summarization and the static cost is set to the maximum value, 16,777,215, the range is not advertised. Setting this static cost is equivalent to configuring a range with the not-advertise option. A summary LSA with this metric (LSInfinity) cannot be advertised, according to RFC 2328 section 12.4.3. This behavior is consistent with the industry standard. If an area range is configured for type 7 to type 5 translation, a type 5 LSA is sent if the metric is set to 16,777,215; however, other routers will not compute a route from a type 5 LSA with this metric. See "Configuring the Static Area Range Cost" on page 1020 for a configuration example. 948 Configuring OSPF and OSPFv3