An engineer is attempting to improve OSPF network performance and discovers that the
entire SPT recomputes whenever a type 1 or type 2 LSA is received within an area. Which action can
optimize SPT operations?
A. Tune LSA throttling thresholds.
B. Enable incremental SPF.
C. Configure totally stubby areas throughout the domain.
D. Summarize networks on all ABRs.
Answer: B
Explanation:
https://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/ospfispf.html#wp1027184
"Benefits of OSPF Incremental SPF OSPF uses Dijkstra's SPF algorithm to compute the
shortest path tree (SPT). During the computation of the SPT, the shortest path to each
node is discovered. The topology tree is used to populate the routing table with routes to IP
networks. When changes to a Type-1 or Type-2 link-state advertisement (LSA) occur in an
area, the entire SPT is recomputed. In many cases, the entire SPT need not be
recomputed because most of the tree remains unchanged. Incremental SPF allows the
system to recompute only theaffected part of the tree. Recomputing only a portion of the
tree rather than the entire tree results in faster OSPF convergence and saves CPU
resources. Note that if the change to a Type-1 or Type-2 LSA occurs in the calculating
router itself, then the full SPT is performed.Incremental SPF is scheduled in the same way as the full SPF. Routers enabled with incremental SPF and routers not enabled with incremental SPF can function in the same internetwork."
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