Unequal cost load-sharing (IOS Hints)

Unequal cost load-sharing (Cisco IOS hints and tricks)
One of the most commonly asked load-sharing-related questions is "can I load-share traffic across unequal-cost links". In general, the answer is no. In order to load-share the traffic, you need more than one path to the destination and the only way to get multiple routes toward a destination in the IP routing table is to make them equal-cost (the only notable exception being EIGRP that supports unequal-cost load-sharing with the variance parameter).There are, however, two cases where you can force unequal traffic split across equal-cost paths toward a destination: when using inter-AS BGP with the link bandwidth parameter and when using unequal-bandwidth traffic-engineering tunnels.

see also:
Perfect Load-Balancing: How Close Can You Get?
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