В CCNA 7.0, в теме Synchronizing OSPF Databases у Cisco есть следующий слайд:
"2. Exchange DBDs
In the Exchange state, the two routers exchange one or more DBD packets. A DBD packet includes information about the LSA entry header that appears in the LSDB of the router. The entries can be about a link or about a network. Each LSA entry header includes information about the link-state type, the address of the advertising router, the cost of the link, and the sequence number. The router uses the sequence number to determine the newness of the received link-state information.
In the figure, R2 sends a DBD packet to R1. When R1 receives the DBD, it performs the following actions:
It acknowledges the receipt of the DBD using the LSAck packet.
R1 then sends DBD packets to R2.
R2 acknowledges R1."
Что является ошибкой, как с точки зрения RFC 2328, так и фактической реализации Cisco. 🧐