Just search your favorite search engine for the topics mentioned
like this. I searched ospf dr and bdr elections
Understand Open Shortest Path First (OSPF) - Design Guide
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
as for books, I would recommend
Cisco Press - CCIE Professional Development Routing TCPIP, Volume I.
you can find it online somewhere if you look hard enough.
like this. I searched ospf dr and bdr elections
Understand Open Shortest Path First (OSPF) - Design Guide
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html
as for books, I would recommend
Cisco Press - CCIE Professional Development Routing TCPIP, Volume I.
you can find it online somewhere if you look hard enough.