Thanks for the question! The cisco routers can load-balance in one of two ways: on a per-packet basis or a per-destination basis.
We can configure it to do it per destination, this means that all packets heading to destination 188.8.131.52 will send all packets along a single path; then packets heading to 184.108.40.206 will be sent to another path to it's destination. This insures all packets going to a destination will arrive in the sequence sent. Only if there is congestion towards the orginal destination will the second path be used.
We can also configure it to use per packet load-balancing. This serially destributes each packet among all the equal cost routes to the destination. This insures that data is equally distributed across equal-cost paths.
The way the router handles it depends on how the switching for the IP proccess is handled by the router itself.
here is a fuller explanation from Cisco site:
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