Which trunk encapsulation defines one VLAN on each trunk as a native VLAN?

A.
ISL

B.
IEEE 802.1q

C.
IEEE 802.11a

D.
auto

Explanation:
IEEE 802.1q defines one VLAN on each trunk as the native VLAN.
The default value of a native VLAN is VLAN1. The IEEE 802.1q method does not encapsulate frames when
forwarded over a trunk in a native VLAN; that is, IEEE 802.1q does not add its header information while
transmitting frames in the native VLAN. This traffic is called untagged traffic. Frames originating from other
VLANs, however, will have a 4-byte 802.1q header inserted into the frame to identify the VLAN number.
The native VLAN number can be changed if desired. If done it should be done on both ends of the connection.
Otherwise, traffic that uses the native VLAN (untagged traffic) will not be able to cross the link. The commend
to change the native VLAN is
Switch(config)#switchport trunk native vlan vlan number
Inter Switch Link (ISL) does not define one VLAN on each trunk as a native VLAN. ISL is the Cisco proprietary
trunk encapsulation, and it can only be used between two Cisco switches.
IEEE 802.11a is a wireless standard defined by the IEEE, and has nothing to do with VLANs.
Auto is not an encapsulation method. The auto trunking mode is a method for negotiating an encapsulation
method over trunk links.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Configure and verify Layer 2 protocols