Protocols involved in configuring trunking on a switch Considering common Cisco switching terminology, which items below are actually used for VLAN trunking encapsulation or trunk configuration on a switch (select the correct combination from the list: VLAN Trunk Protocol, VLAN 802.1Q, ISL)?

Introduction / Context:
Trunking allows multiple VLANs to traverse a single physical link. Two well-known VLAN trunk encapsulations exist historically on Cisco gear: IEEE 802.1Q (open standard) and Cisco ISL (proprietary, largely deprecated). It is important to distinguish encapsulation protocols from management or distribution protocols like VTP.

Given Data / Assumptions:

• The list includes: 1) VLAN Trunk Protocol, 3) VLAN 802.1Q, 4) ISL.
• We are asked which are used to configure trunking (that is, frame encapsulation on trunk ports).

Concept / Approach:

Trunk encapsulation is about how frames are tagged across a trunk. IEEE 802.1Q inserts a tag in the Ethernet frame; ISL encapsulates the entire frame in a Cisco header. VTP, despite its name (VLAN Trunk Protocol), is not an encapsulation; it distributes VLAN database information and does not determine the tagging method on trunks.

Step-by-Step Solution:

Verification / Alternative check:

On Cisco IOS, trunk encapsulation configuration uses switchport trunk encapsulation dot1q or isl (where supported). VTP is configured separately and does not appear in the encapsulation command.

Why Other Options Are Wrong:

• 1 only or 1,3,4: Includes VTP, which is not a trunk encapsulation protocol.
• 3 only: Excludes ISL, which has historically been used for trunk encapsulation.
• 2 and 3 only: Item 2 is not part of the presented list in the prompt and is irrelevant here.

Common Pitfalls:

• Assuming VTP configures or negotiates the trunk encapsulation; it does not.
• Confusing DTP (Dynamic Trunking Protocol) with VTP; DTP negotiates trunk formation, not encapsulation.

Final Answer:

3 and 4