In the Diagram below when R1 is newly added to Network Topology R1 and R2 become neighbors and exchange Type 1 LSA from R2, R3, R4. But how R1 knows Network LSA created by the DR in LAN(subnet 1). Does R2 forward the TYPE 2 LSA learned from DR?
DR and BDRs are only used on broadcast networks. The network to the right of R2 is a broadcast network, so it has DR and BDR routers, and all the other routers only exchange routing information with the DR and BDR routers on that network.
The network to the left of R2 is a point-to-point link, wo there are no DR or BDR routers on that link. Both the routers on that link form adjacencies and exchange routing information.
Every router in an area knows about every other router and networks in the area. To do this, R2 will tell R1 about everything it knows because it is a peer to R1 on that network. On the broadcast network, it will only tell the DR and BDR about what it learns from R1. It is up to the DR and BDR to spread that information to any DROTHER routers on the broadcast network.