OSPF DR & BDR Election on MikroTik

We are starting a new section, and in this section, I will be discussing the DR and BDR, which stand for Designated Router and Backup Designated Router.

Understanding DR and BDR

Let’s first understand what the Designated Router and Backup Designated Router are, and why they are necessary in OSPF.

In OSPF, routers are constantly sharing information with one another to build a dynamic and accurate map of the network. This allows OSPF to ensure each router knows the best path to every other part of the network. However, in networks with many routers, this constant communication can create a lot of data traffic, particularly if all routers were to communicate updates directly to every other router.

To make this easier to understand, let me give you an example. Assume we have a scenario where all routers are connected to a switch, and they are within Area 0

This configuration is considered a broadcast network, meaning that OSPF routers in the same area can directly communicate with each other by sending packets that are accessible to all routers in that network segment. If we enable OSPF on all routers in this network, they will form neighborships by sending Hello packets to each other. When neighborships are formed, the routers will start exchanging LSAs (Link-State Advertisements) to update each other about their network segments and any changes.

Imagine now that every router has to send LSAs to all other routers in the network individually. This means each router would send its updates to every other router, resulting in a large number of LSA exchanges that grow rapidly with each new router added to the network. The formula for calculating the number of LSA exchanges is: