as far as i know, there are 2 types of load balancing. In general, load balance occurs when there are multiple paths with the same metrics to the specific network in the routing table from the same routing protocol. You can configure per-packet or per-destination load balancing.
Deffault setting on Cisco devices, packets to one destination of specific network will take one path, packets to other destination of the same network will take second. This load balance uses route-cache so it offers fast balancing.
You can configure it on interface:
Router(config-if)#no ip route-cache
Router will now look at each packet and equally load balance them between paths. This type is much more cpu expensive, so low-end devices propably will not handle it properly. It is not recommended for them.
If CEF is in use on router, there are different commands. You can find them in this Cisco Document
In routing protol such as EIGRP you can use variance command to set uequal load balancing. It means, EIGRP will load balance also in case of several paths to same network but with different metrics. Variance itself is number - multiplicator. How many times can path have worse metrics as the lovest metrics to that destination in table.
For further informations about load-balancing you can also try to read these documents
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