Manipulating OSPF DR and BDR Election on MikroTik Routers

Today, I am diving into a fascinating and essential topic in OSPF (Open Shortest Path First) networking: the DR (Designated Router) and BDR (Backup Designated Router) election process. As someone passionate about explaining networking concepts clearly, I will take you step by step through the lab setup, theoretical background, and practical implementation of this process using MikroTik routers.

Lab Setup

The lab setup involves two MikroTik routers connected via a broadcast network. In OSPF, a broadcast network is one where multiple routers share the same network segment and can communicate with one another. This setup requires a DR and a BDR to reduce the number of adjacencies formed. Instead of every router communicating directly with every other router, they all communicate with the DR, which then shares information with the other routers, including the BDR. The BDR acts as a backup in case the DR fails.

Step 1: Identifying the Current DR and BDR

In my lab, I have two routers:

Router 1 has a Router ID of 1.1.1.1.
Router 2 has a Router ID of 2.2.2.2.

Both routers are connected on a broadcast network with default OSPF configurations. Since their priorities are identical at 128, the election process defaults to the Router ID. As Router 2 has the higher Router ID (2.2.2.2), it is elected as the DR, and Router 1 (1.1.1.1) becomes the BDR. Let’s verify this using MikroTik commands:

[admin@Router1] > /routing/ospf/interface/print
Flags: X – disabled, I – inactive, D – dynamic, P – passive
Columns: INTERFACE, COST, PRIORITY, NETWORK-TYPE, STATE, DR, BDR
# INTERFACE COST PRIORITY NETWORK-TYPE STATE DR BDR
0 ether1 10 128 broadcast BDR 192.168.1.2 192.168.1.1

The output confirms that Router 1 is the BDR. Its STATE is labeled as BDR, and the DR is shown as 192.168.1.2 (Router 2).

Now, let’s check Router 2: