350-401 Question #569: Real Exam Question with Answer & Explanation

Question

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?

Options

• ASwitch 1(config)#interface gig1/0/20
• BSwitch2(config)#interface gig1/0/20
• CSwitch2(config)#interface gig1/0/20
• DSwitch1(config)#interface gig1/0/20

Explanation

The issue of a non-functional trunk between switches is resolved by explicitly configuring 802.1Q trunking mode and encapsulation on both interfaces.

Common mistakes.

• A. 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.
• C. 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.
• D. 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.

Concept tested. Trunking mode and encapsulation configuration

Reference. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/consolidated_guide/b_consolidated_3se_3850_cg/b_consolidated_3se_3850_cg_chapter_01000.html

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