CCNA Plan

CCNA practice question: Network Access

Network AccessDifficulty 2/5

Two switches are connected by an 802.1Q trunk. Switch A has native VLAN 1, switch B has native VLAN 99. What is the result?

  1. AThe trunk fails to form
  2. BCDP reports a native VLAN mismatch and untagged frames leak between VLAN 1 and VLAN 99
  3. CAll VLANs are tagged, so nothing changes
  4. DSTP blocks the trunk permanently
Show answer and rationale

Correct: B. 802.1Q sends native-VLAN frames untagged. With mismatched native VLANs, each switch places the other's untagged frames into a different VLAN, effectively bridging VLAN 1 and 99, and CDP logs a mismatch warning. The trunk still comes up.

  • A — The trunk forms; the mismatch is a configuration error, not a trunk-negotiation failure.
  • C — The native VLAN is exactly the VLAN that is not tagged.
  • D — STP may detect inconsistency on PVST+ but does not permanently block by default in this scenario.

Concept being tested

VLANs and trunking, EtherChannel, Rapid PVST+, Cisco wireless architectures and WLAN configuration, physical infrastructure connections. — 20% of the exam. Study guide for Network Access.

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Primary references

  1. CCNA Exam v1.1 (200-301) Exam Topics — Cisco Systems · primary · retrieved 2026-09-21, verified 2026-09-21
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