What does DR mean?
Among all the routers on a given segment, the one with the greatest priority is known as the Designated Router (DR). You can set the priority manually or leave it at one of the predefined values; it can take on a value between zero and 255. In a situation when multiple routers are equally important, the router with the highest router ID (often the highest IP address) takes over as the DR. The primary roles of the DR are:
- It links up with all the other OSPF routers on the same segment. An adjacency is a formal link between two OSPF routers that lets them swap routing information.
- Links-state updates (LSUs) are sent to all OSPF routers on the same network segment through this DR which acts as a Hub. With an LSU, you can find out about the status of your router’s ports and neighbors.
It is the responsibility of the DR to keep a comprehensive link-state database (LSDB) of the network segment. This database includes all of the LSUs that have been received from various routers. Additionally, the DR is responsible for the generation of a network LSA for the network segment. This LSA is a summary of the information provided by all of the routers that are linked to it. A flood of the network-LSA is sent to all of the different OSPF routers that are located within the same area.
What does BDR mean?
It is the router that has the second highest priority among all of the routers on the segment and serves as a backup for the Destination Router (DR). The Backup Designated Router (BDR) is the router that is designated to be used on a segment. The BDR is chosen after the DR, and the election process is identical to that of the DR. Within the BDR, there are two crucial functions:
- On the same network segment, it creates adjacencies with the DR and every other OSPF router. The DR provides all of the LSUs to the BDR, which then synchronizes the LSDB with it.
- If the DR malfunctions or is rendered inaccessible, it assumes control of the DR’s duties. After that, the BDR becomes the new DR and begins creating and dispersing network LSAs for the network segment.
Although it is elected simultaneously with the DR, the BDR will not carry out any function until the DR fails.
We can now grasp OSPF’s DR and BDR concepts with more clarity. First, we’ll go over how to elect DRs and BDRs.
The OSPF election process for DR and BDR
Two main factors—the OSPF priority and the router ID—form the basis of the DR and BDR election.
