Imagine my environment is all Cisco switches. If my intention is to assure that dot1q is my encapsulation protocol when on trunking mode, is it necessary to do:
switchport mode trunk
switchport trunk encap dot1q <===
switchport trunk allow vlan (...)
In my environment the line 'switchport trunk encap dot1q' is not present in switches. I just want to confirm that is not necessary and DTP would negotiate encapsulation dot1q by default, always? From reading the documentation so far, it is not clear to me if certain platforms could pick ISL as a default, in case 'trunk encapsulation dot1q' is not specified.
Some Layer 2 switches, such as the 2950 and 2960 series switches, support 802.1Q only therefore the commands "switchport trunk encapsulation dot1q" will not be accepted.
Hope this helps.