Hello Zaman
This is a very good question! Shows you’re thinking very analytically. So, changes in LSA types 1 and 2 will always trigger a full SPF calculation unless the Incremental SPF is enabled. Changes in LSA types 3, 4, 5 and 7 will trigger what is called a partial SPF which is different than an incremental SPF calculation. A partial SPF calculation only involves the leaves of the SPF tree. Any changes in these LSAs indicate changes ONLY in the leaves. The SPF tree itself remains unchanged with changes to these LSAs. This is the default behaviour of a Cisco OSPF router.
So to specifically answer your question, yes, incremental SPF will be triggered only with changes to LSA types 1 and 2.
To be a little more clear as to the difference between Incremental and partial SPF, here’s a more detailed explanation of the difference.
* Partial SPF involves changes only to the leaves. No links are changed.
* In Incremental SPF, the SPF tree will be changed to discover an alternative best path after a link failure. The farther the incremental SPF is run from the root of the tree, the more savings in time and resources compared to a full SPF. If the change is close to the root, there is little performance improvement over full SPF.
I hope this has been helpful!
Laz