How is the load shared between two parallel lines of equal capacity when these lines are configured for load balancing?

For IP, if the cisco router is fast switching, it load balances on a per-destination basis. If the router is process switching, it load balances on a per-packet basis. For more information, refer to How Does Load-Balancing Work? Cisco IOS® Software also supports both per packet and per destination load balancing with Cisco Express Forwarding (CEF). For more information, refer to Load Balancing with CEF and Troubleshooting Load Balancing Over Parallel Links Using Cisco Express Forwarding.