When configuring a load balancer on a MikroTik device, using administrative distances (AD) on default routes can be a crucial tool in determining how the router handles multiple routes to the same destination.

Administrative distance is a metric used to prefer one route over another when there are several possible routes to the same destination. A lower administrative distance has higher priority over a higher one.

In a load balancing scenario, you can have multiple egress routes (for example, through different Internet connections) configured on the MikroTik device. This is where administrative distances play an important role:

• No need for different distances for basic balancing: For basic load balancing configurations where you want traffic to be distributed equally across multiple WAN connections, it is not strictly necessary to assign different administrative distances to each route by default. MikroTik can handle load balancing using other methods, such as PCC (Per Connection Classifier), without the need to modify administrative distances.
• Using different distances for redundancy or failover: Administrative distances become relevant in scenarios where you want to implement redundancy or failover in addition to load balancing. In these cases, assigning different administrative distances to the default routes allows the router to decide which route to use preferably and which to use in case the primary route fails. For example, you could configure a primary WAN connection with a lower administrative distance (for example, AD=1) and a backup connection with a higher distance (for example, AD=2). This way, under normal conditions, all traffic would be directed through the main connection, but if it fails, the router would automatically start using the backup connection.

Conclusion

The decision to use different administrative distances in the default routes within a load balancing context in MikroTik depends on the specific objectives of your network:

• For pure load balancing (equitable traffic distribution), it is not necessary to assign different administrative distances to the default routes.
• To implement redundancy or failover Along with load balancing, assigning different administrative distances to default routes is a recommended practice to ensure that traffic is automatically rerouted via the alternate route in the event of a primary connection failure.

In any case, load balancing and route management configuration must be carefully planned and tested to ensure that the network operates as expected under various conditions.