Refer to the exhibit. A frame on VLAN 1 on switch S1 is sent to switch S2 where the frame is received on VLAN 2. What causes this behavior?

The correct answer is C. native VLAN mismatches. A native VLAN mismatch is the cause. On an 802.1Q trunk link, frames belonging to the native VLAN are sent untagged. If S1 has its native VLAN set to VLAN 1 and S2 has its native VLAN set to VLAN 2, then frames sent untagged by S1 (as VLAN 1 traffic) will be received and processe

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Question

Refer to the exhibit. A frame on VLAN 1 on switch S1 is sent to switch S2 where the frame is received on VLAN 2. What causes this behavior?

Options

Atrunk-mode mismatches
Ballowing only VLAN 2 on the destination
Cnative VLAN mismatches
DVLANs that do not correspond to a unique IP subnet

How the community answered

(22 responses)

A
14% (3)
B
5% (1)
C
73% (16)
D
9% (2)

Explanation

A native VLAN mismatch is the cause. On an 802.1Q trunk link, frames belonging to the native VLAN are sent untagged. If S1 has its native VLAN set to VLAN 1 and S2 has its native VLAN set to VLAN 2, then frames sent untagged by S1 (as VLAN 1 traffic) will be received and processed by S2 as VLAN 2 traffic-because S2 assigns all untagged frames to its own native VLAN (2). This cross-VLAN frame delivery without intentional routing is the classic symptom of a native VLAN mismatch. This is a security concern and can be exploited for VLAN hopping attacks. Cisco recommends setting the native VLAN to an unused VLAN to avoid this issue.

Topics

#native VLAN mismatch#trunk#VLAN#VLAN hopping

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