Examkin

Question

Difficulty: MediumVLAN Configuration and 802.1Q Trunking

A network engineer is configuring an IEEE 802.1Q trunk link between two switches, SW-DIST-01 and SW-ACCESS-02. Switch SW-DIST-01 has port GigabitEthernet1/0/1 configured with 'switchport trunk native vlan 99'. Switch SW-ACCESS-02 has port GigabitEthernet0/1 configured as a trunk using the default native VLAN (VLAN 1). Which of the following statements accurately describe the operational impact of this configuration or the steps required to resolve it? (Select TWO.)

  1. Untagged frames transmitted from VLAN 99 on SW-DIST-01 will be improperly received into VLAN 1 on SW-ACCESS-02.Answer
  2. B
    Tagged VLAN traffic, such as VLAN 20 and VLAN 30, will be automatically blocked across the trunk until the native VLAN mismatch is resolved.
  3. Executing 'switchport trunk native vlan 99' on interface GigabitEthernet0/1 of SW-ACCESS-02 will align both ends and eliminate cross-VLAN traffic leakage.Answer
  4. D
    Changing the port mode on SW-DIST-01 to switchport mode access will maintain trunking capabilities while resolving the tag mismatch.

Answer

Untagged frames transmitted from VLAN 99 on SW-DIST-01 will be improperly received into VLAN 1 on SW-ACCESS-02, and executing 'switchport trunk native vlan 99' on interface GigabitEthernet0/1 of SW-ACCESS-02 will align both ends and eliminate cross-VLAN traffic leakage.
On an IEEE 802.1Q trunk, frames belonging to the native VLAN are transmitted without an 802.1Q tag header. When a native VLAN mismatch exists between two switches, untagged traffic sent by one switch is placed into whichever native VLAN is configured on the receiving switch port, causing cross-VLAN frame leakage. Aligning the native VLAN configurations on both trunk ports ensures consistent frame interpretation and resolves the mismatch.

Step-by-Step Solution

1
Analyze 802.1Q native VLAN frame encapsulation behavior across trunk endpoints.
802.1Q trunks leave native VLAN frames untagged. When SW-DIST-01 sends untagged VLAN 99 frames, SW-ACCESS-02 receives them on a port expecting VLAN 1 to be untagged, misplacing the frames into VLAN 1.
Trunk links do not insert an 802.1Q tag header for frames belonging to the configured native VLAN.
2
Determine the effect of a native VLAN mismatch on tagged VLANs traversing the trunk.
Frames with explicit 802.1Q tags (VLAN 20, VLAN 30) are correctly identified and processed by both switches based on their tag headers.
Native VLAN mismatch affects only untagged traffic and control plane protocols; tagged traffic is processed independently based on the 4-byte 802.1Q header.
3
Identify the proper remediation command.
Configuring matching native VLAN IDs (VLAN 99) on both trunk interfaces aligns ingress and egress frame processing.
Matching native VLAN configurations prevent VLAN leaking and clear STP/CDP native VLAN mismatch warnings.

Key Concept

802.1Q Trunking Native VLAN Mismatch Consequences and Configuration Alignment
Estimated Time:1m 30s
Rate this question

Topics

VLAN Configuration and 802.1Q Trunking

More questions from this topic