OSPF - BDR is elected before DR

The OSPF protocol specifies the election process and the election criteria for the Designated Router (DR) and Backup Designated Router (BDR) election

The RFC that defines OSPF (2328) specifies this process. According to this RFC, the BDR is typically elected first, followed by the election of the DR. The complexity of this election algorithm ensures an orderly transition from BDR to DR when the current DR fails. This is achieved through hysteresis, which prevents the election of a new BDR until the old BDR has accepted its new DR responsibilities.

However, it is important to note that not all vendors strictly adhere to the RFC. Vendors like Cisco and Juniper may implement additional mechanisms, enhancements, and rules that deviate from the RFC to suit their specific needs while maintaining compatibility with other vendors.

https://networklessons.com/ospf/ospf-drbdr-election-explained/ https://datatracker.ietf.org/doc/html/rfc2328#section-9.4