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Does OSPF Discard Routes During DR Re-election?

No, routers do not discard all IP routes learned through OSPF during a DR re-election. The OSPF process is designed to handle DR re-election smoothly without disrupting the entire network's routing table. Here’s what happens during the process:

  • OSPF Neighbor Relationships: When a DR re-election occurs, only the OSPF neighbor relationships with the DR and Backup Designated Router (BDR) are affected. Other routers maintain their adjacencies and routing information.

  • Routing Table Retained: The OSPF routing table remains intact during a DR re-election. Routes learned via OSPF, which have already been installed in the routing table, are not discarded unless a topology change affects them (e.g., a failure or a new LSA indicating a different path).

  • LSA Synchronization: The newly elected DR (or BDR) will synchronize LSAs with its neighbors. The OSPF database is re-synchronized, but this does not mean routes are discarded. The synchronization ensures that all routers on the network segment have an updated Link-State Database (LSDB).

In short, OSPF routers retain the routes learned through OSPF, and only the re-synchronization process occurs when DR re-election happens. This minimizes disruption to routing in the network.

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