Jeff Doyle (TCP/IP) vol 1 states that the adjacency building process uses 3 types of OSPF packets:
Database Description (type 2)
Link State Request (type 3)
Link State Update (type 4)
However, RFC 2328 States that adjacencies are formed by Type 2 and Type 3 only. Can I take this as an error by Doyle ?
Actually Vlad, LS Acks are not used in the Database Exchange process. Each router places all requested LSAs in the LSA Request List. As LS Updates are received, LSAs in the LSA Request List. If an LSA has not been received, the LS Request packet will be re-transmitted.
As such, LS Acks are not used here but they are certainly used as part of the reliable flooding mechanism.
I would appreciate you rating the post if it helps.