01Plain English
The simple explanation
The designated router describes the routers attached to a shared transit network.
02Under the hood
The technical explanation
The DR originates a Network LSA for a broadcast or NBMA transit network when it has a full adjacency on that network. It lists attached routers fully adjacent to the DR, including the DR itself. The Link State ID is the DR’s interface IP address. Flooding stays within the area.
Protocol reference: RFC 2328 (OSPFv2). NSSA reference: RFC 3101.
logic
Make it stick
The group-project spokesperson who actually knows who turned up.
03On the wire
Example
A shared Ethernet segment can appear as a network vertex in the SPF graph. A point-to-point link does not need a DR or Type 2 LSA.