Refer to the exhibit. The trunk does not work over the back-to-back link between Switch1 interface Giq1/0/20 and Switch2 interface Gig1/0/20. Which configuration fixes the problem?

While `dot1q` is correct for encapsulation, `switchport mode dynamic auto` on Switch1 might not form a trunk if the peer is also `dynamic auto` (resulting in access mode) or not explicitly configured for trunking.

The commands `switchport mode trunk` and `switchport trunk encapsulation dot1q` explicitly configure the interface for 802.1Q trunking, ensuring that the link will form a trunk. This addresses common issues where a trunk fails due to mismatched trunking modes (e.g., dynamic auto on both sides resulting in access mode) or incorrect encapsulation types.

Configuring `switchport mode access` on Switch2 will prevent the interface from forming a trunk, as access ports are designed for end devices and carry traffic for a single VLAN.

Configuring `switchport mode access` on Switch1 will prevent the interface from forming a trunk, as access ports are designed for end devices and carry traffic for a single VLAN.