DR refers to the designated router. BDR refers to the backup designated router. DR other refers to the router that is neither DR nor BDR. The DR can broadcast the network link status to all the routers on the network.

The rules for electing a DR are as follows:

1. After an interface becomes Up, routers send Hello packets and at the same time enter the waiting state. In this case, the waiting timer is generated and its value is the same as the value of the dead timer. The value defaults to 40s and cannot be adjusted.

2. Before the waiting timer is triggered, the sent Hello packets do not contain the DR or BDR fields. During the waiting period, if the received Hello packets contain the DR or BDR field, the election is not triggered and routers directly leave the waiting state to start neighbor synchronization.

3. Assume that a DR and a BDR already exist on the network. In this case, the router that is newly added to the network does not change the existing DR or BDR regardless of the value of its router ID.

4. When the DR becomes Down because of a fault, the BDR takes over the role of the DR and the remaining devices whose priority is larger than 0 compete to become the new BDR.

5. The DR is elected based on the following rules only when routers with different router IDs or DR priorities become Up and perform DR election at the same time. The DR election rules include: The router with the highest DR priority becomes the DR, and the router with the second highest DR priority becomes the BDR. The router with DR priority 0 can only be a DROther. If the routers have the same DR priority, the router with the largest router ID becomes the DR, the router with the second largest router ID becomes the BDR, and other routers become DR others.
Huawei MA5683T, Huawei MA5608T, Huawei OSN3500