What happens when the designated router (DR) fails?

When the designated router (DR) fails in an OSPF network, the backup designated router (BDR) automatically assumes the role of the DR. This is a critical function of OSPF's design to maintain network stability and efficiency in the routing process.

The DR is responsible for generating and distributing link-state advertisements (LSAs) for the broadcast and non-broadcast multi-access networks. When the DR fails, the BDR takes over this responsibility without requiring any manual intervention or causing disruption to the network's operation. This seamless transition helps ensure that OSPF can continue to function effectively, and it maintains the integrity of the network topology information.

In contrast to what happens when the DR fails, the network does not collapse, and routers do not shut down or reset their routing tables. The idea of a complete network collapse would imply a more serious failure that could affect all routers, which is not the case here. Instead, OSPF's redundancy mechanisms, like the BDR, are specifically designed to prevent such complete failures. Therefore, the ability of the BDR to take over as the DR is crucial for maintaining the continuity and reliability of the OSPF routing process.