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When configuring a trunking EtherChannel between two switches, it’s important to understand the key requirements for a successful setup. Among the options you’ve listed, the correct requirement is:

• The allowed range of VLANs must be the same on both switches.

This is essential because EtherChannel aggregates multiple physical links into a single logical link for increased bandwidth and redundancy. When it’s configured as a trunk, both ends of the EtherChannel must allow the same range of VLANs for consistent data traffic flow across the trunked links.

The other options are not requirements for trunking EtherChannel:

1. Participating interfaces being physically contiguous on a switch: This is not a requirement. Interfaces in an EtherChannel can be non-contiguous.
2. Participating interfaces being on the same module on a switch: This is also not a requirement. Interfaces from different modules on a modular switch can be part of the same EtherChannel.
3. Participating interfaces assigned the same VLAN number: This is not applicable for a trunking EtherChannel. Trunk ports carry traffic from multiple VLANs, not just a single VLAN.

In addition to matching VLAN configurations, other common requirements for EtherChannel configuration include setting the same speed and duplex settings on all participating interfaces, and ensuring that all interfaces are either all trunk ports or all access ports. Configuration consistency across all these parameters is crucial for the proper functioning of an EtherChannel.