Disabling and Reenabling Incremental SPF

By default, when changes occur to a type 3, type 4, type 5, or type 7 LSA, OSPF recalculates new, loop-free routes for only the LSAs that change. When a subset of summary and external LSAs in the external link-state database change, a full SPF recalculation is not necessary. However, through the CLI, you can disable the incremental SPF calculation so that the router can perform a full SPF calculation on all external and summary LSAs in the link-state database.

Note: If a full SPF calculation is scheduled for the area when the summary LSA is received, then the incremental SPF calculation is not performed even though the incremental SPF calculation is enabled for the summary LSAs. The incremental SPF calculation for summary LSAs is applicable only for OSPFv2.