In some cases, non-backup areas cannot be physically connected to the backbone area. You can configure a virtual link for an ABR that is not directly connected to the backbone area to establish a tunnel to the backbone area.
You can configure DR priorities of routers for DR election on a broadcast or non-broadcast network. Generally, the router with high performance and reliability is elected as a DR/BDR.
If there are multiple paths with the same cost destined for the same destination, load balancing among equal-cost routes can be configured to load balance IP packets among these paths, which increases the link utilization.
To import external routes to the OSPF routing table and still keep other stub area features, the network administrator can configure the area as the NSSA area.
In certain cases, the direct physical connection between a backbone area and a non-backbone area can hardly be realized. In this case, you can configure OSPF virtual links for the ABR that is not directly connected to the backbone area.
On both broadcast and non-broadcast networks, you can configure the DR priorities of OSPF interfaces to impact the DR/BDR election. In common cases, the router with high performance and reliability is selected as the DR/BDR.
When there are several paths of the same cost to one destination, you can configure the load balancing of equal-cost routes. In this way, load balancing is implemented on these links, thus improving the link usage.