EIGRP load balancing over equal-cost paths

When router learned routes from other routing protocols, it will choose a best route to install to routing table. This route is the route with lowest  Administrative Distance, this value is assigned to each routing protocol.
In case there are multiple routes learned from a single routing protocol, metric will be considered and route with the lowest metric wins. If those routes have the same metric values, load balancing can be occur (EIGRP, OSPF). EIGRP even allows load balance over unequal-cost paths.

By default, EIGRP will load balance over 4 equal-cost paths and can be increased to 16 paths. EIGRP does not perform load balancing by itself, switching technologies handle it.

CEF is a layer 3 switching technology and enabled by default on IOS, and when CEF is enabling, load balancing will occur on per-destination basis. That means, all packets reach to a destination will use the same output interface.

In topology table:

R1#show ip eigrp to
IP-EIGRP Topology Table for AS(10)/ID(1.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status
...
P 3.3.3.0/24, 2 successors, FD is 435200
        via 10.0.0.2 (435200/409600), Ethernet0/0
        via 13.0.0.2 (435200/409600), Ethernet0/1
...

There are two successor routes to reach 3.3.3.0/24 from R1 with the same FD 435200. In this case, CEF is enabled on R1. so load balancing will occur in per-destination basis.

R1#show run | section cef
ip cef

 In per-destination basis, all traffics reach a destination will use the same output interface:

 When cef is disabled, packets are distributed over both two routes:

 Alternatetively, per-packet load balancing can be happen while CEF is enabled by configuring load sharing on outgoing interfaces.

R1(config)#ip cef
R1(config)#int e0/0
R1(config-if)#ip load-sharing per-packet
R1(config-if)#int e0/1
R1(config-if)#ip load-sharing per-packet