Only Cisco switch platforms that still support isl trunking need to have the trunking protocol configured.

Newer platforms have no support for isl trunking anymore, so the interface command switchport trunk encapsulation dot1q is default/implicit/unsupported, and there's no need to configure it. Just set switchport mode trunk.

Of the ones that still support isl, Cat3750, 3550, 3560 spring to mind, and the Cat4000 and Cat4500 Series (incl their 4900M and 4948 cousins), and probably a few of the older ones, too.

I couldn't say when ISL trunking support was dropped from the 2950/2960G/2960-S/2960-X product line. It's just a matter of trying. If the switchport won't accept switchport mode trunk, then setting the trunking encapsulation is probably needed.

Only Cisco switch platforms that still support isl trunking need to have the trunking protocol configured.

Newer platforms have no support for isl trunking anymore, so the interface command switchport trunk encapsulation dot1q is default/implicit/unsupported, and there's no need to configure it. Just set switchport mode trunk.

Of the ones that still support isl, Cat3750, 3550, 3560 spring to mind, and the Cat4000 and Cat4500 Series (incl their 4900M and 4948 cousins), and probably a few of the older ones, too.

EDIT: the following section is incorrect as it seems that the 29xx range never had support for isl trunking at all.

I couldn't say when ISL trunking support was dropped from the 2950/2960G/2960-S/2960-X product line.

Eventually, it's just a matter of trying. If the switchport won't accept switchport mode trunk, then setting the trunking encapsulation is probably needed.