Exchange with a Designated Router
Database exchange with a DR differs slightly than database exchange when no DR exists. The majority of the process is similar, with the same messages, meanings, and neighbor states. The big difference is the overriding choice of with whom each router chooses to perform database exchange.
Non-DR routers do not exchange their databases directly with all neighbors on a subnet. Instead, they exchange their database with the DR. Then, the DR exchanges any new/changed LSAs with the rest of the OSPF routers in the subnet.
The concept actually follows along with the idea of a Type 2 LSA as seen earlier in Figure 8-4. Figure 8-9 represents four Type 1 LSAs, for four real routers on the same LAN, plus a single Type 2 LSA ...