Cisco (350-401-ENCOR) Exam Questions And Answers page 16

Most likely, the router will exchange its entire database with the designated router (DR) if the output of the show ip ospf neighbor command reveals that the router s Open Shortest Path First (OSPF) state is FULL/ DR. This output indicates that the router has formed a full adjacency with its neighbor and that the neighbor is the DR. This output also indicates that the router is configured on a multiaccess network because OSPF routers that are connected in a pointtopoint fashion do not elect a DR or BDR. The neighbor states for a multiaccess OSPF router include all of the following:
- FULL/DR
- FULL/BDR
- 2WAY/DROTHER
On a multiaccess network, OSPF routers exchange databases only with the DR and BDR, which helps prevent congestion. Therefore, routers with a 2WAY/DROTHER state do not exchange full databases with those neighbors.
The router is not on a pointtopoint network. On a pointtopoint OSPF network, a neighbor state of FULL/indicates that the OSPF neighbors have formed a full adjacency and are thus capable of exchanging their entire databases. Because neither a DR nor a BDR exists on a pointtopoint network, the second field in the state output will be a dash.
The router is neither the DR nor the BDR. The first field in the state output indicates the state of the adjacency. The second field in the state indicates the type of OSPF router to which the router is connected, not the role of the router itself.
The DR generates linkstate advertisements (LSAs) that contain OSPF routing information, and the BDR takes over for the DR if the DR fails. Because only the DR and BDR generate LSAs, network bandwidth is conserved. The DR is typically the router with the highest OSPF priority, and the BDR is typically the router with the secondhighest OSPF priority. If priorities are equal between two or more routers, the router with the highest router ID will be elected. OSPF priorities can range from 0 through 255? the default OSPF priority is 1. A router with a priority of 0 will never become the DR or BDR. A router that is not the DR or BDR will display a state of DROTHER.
Cisco: OSPF Neighbor Problems Explained: Typical Reasons for OSPF Neighbor Problems

RouterA will advertise the routes to 192.168.0.0/24 and 192.168.1.0/24 to RouterB, and RouterB will advertise only the route to 192.168.1.0/24 to RouterD. RouterB will advertise both routes to RouterC because RouterB and RouterC are in the same autonomous system (AS). The neighbor 10.1.1.2 routemap map1 out command applies route map map1 to modify outgoing routes from RouterA. Because the routemap map1 permit 20 command overrides the implicit deny rule for map1, the route map will not restrict which routes are advertised from RouterA to RouterB. Additionally, map1 is configured to only apply the noexport community attribute to routes that match access list 1. Routes that do not match access list 1 are advertised without the attribute. Because route map map1 is configured to apply the noexport community attribute to only the routes that pass access list 1, the noexport community attribute will affect only the route to 192.168.0.0/24.
The neighbor 10.1.1.2 remoteas 200 command specifies that RouterB, which is in AS 200, is an external Border Gateway Protocol (eBGP) neighbor of RouterA. The neighbor 10.1.1.2 sendcommunity command configures RouterA to send community attribute settings to RouterB. The community attribute is an optional, transitive Border Gateway Protocol (BGP) attribute that is not required to be supported by all BGP implementations. Additionally, BGP implementations that do not support the community attribute are not required to pass the attribute to other routers. By default, Cisco routers do not pass community attributes to BGP neighbors. The community attribute can be modified in a route map by issuing the set community command with one of the following four keywords:
-no-advertise -prevents advertisements to any BGP peer
-no-export-prevents advertisements to eBGP peers
-loca-las -prevents advertising outside the AS, or in confederation scenarios, outside the sub-AS internet-advertises the route to any router
The set community no-export command configures the BGP community attribute to inform neighbor routers to not export the route to eBGP peers. Therefore, RouterB will not advertise the route to 192.168.0.0/24 outside of AS 200. Because RouterD is in AS 300, RouterB will not advertise the 192.168.0.0/24 route to RouterD. RouterB will advertise both routes to RouterC, which is in AS 200. The community attribute does not modify how RouterA advertises the routes; it modifies how neighbor routers advertise the routes received from RouterA.
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-bgp-toc.html#communityattribute
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-bgp-toc.html#sec3
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/irg-cr-book/bgp-n1.html#wp2607806244