@AIMS-Informatique:
Why are you telling him to switch from trunk to general
This is due to the way some switchs understand and handle this spécific Trunk mode. And no, Trunk isn't like general, as a Trunk would assume to carry and forward all VLANs, even thoses not configured. So the behavior of a Trunk is slightly different. Generally a Trunk config will be necessary if you plan to enable GVRP.
Plus, for my point of view, it is better to know your network and set up only what needed.
It is true that ciscos switchports in trunk mode can carry all VLANs, but you can also limit them only to specific VLANs with "switchport trunk allowed vlan add XXX,YYY,ZZZ" like I described. This has the effect of making the trunkport only forward traffic for the allowed vlans and discarding any received frames tagged for unconfigured VLANs.