Which load balancing option for iP-only traffic is the least efficient in terms of Layer 2 EtherChnnel physical links utilization?

Per-port-number (Layer 4) hashing incorporates the wide variety of TCP/UDP source and destination port values, distributing traffic across multiple member links effectively even for IP traffic.

When traffic is IP-only and routed through a default gateway, every outbound Ethernet frame carries the same destination MAC address - the MAC of the next-hop router interface. EtherChannel hashing on destination MAC produces an identical hash for every such frame, directing all traffic to one physical member link and leaving all others idle. This completely defeats link aggregation and results in the worst possible bandwidth utilization across the bundle.

Per-destination-IP hashing uses the diversity of destination IP addresses across different flows to spread traffic across links, providing reasonable distribution for routed traffic.

Per-source-IP hashing uses differing source IP addresses from multiple hosts to distribute flows across member links, yielding better utilization than destination MAC in routed environments.