When OSPF do recalculation

1, When there is update of LSA type 1 and type 2, recalculation will be done for the entire routing table,  started with shortest path calculation for each area. not just in the area that link state database has changed.

2, When there is update of LSA type 3, network summary, the recalculation will be done partially. Specially, the destination described in the network summary LSA will be recalculated, if the destination is ABR, it may also need to re-examine all external LSA types.

3, When there is update of LSA type 5 or 7, the destination described in the external LSA will be recalculated.

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