A network engineer observes that hosts on VLAN 10 connected to Switch-Alpha are unexpectedly able to communicate with hosts on VLAN 20 connected to Switch-Beta across an 802.1Q trunk link without traversing a Layer 3 router. Console logs on Switch-Alpha report a CDP native VLAN mismatch warning indicating GigabitEthernet0/1 is in native VLAN 10, while Switch-Beta reports native VLAN 20 on its connecting port. Which of the following technical explanations accounts for this cross-VLAN communication behavior?
- Switch-Alpha transmits frames originating from VLAN 10 without an 802.1Q header across the trunk, and Switch-Beta accepts these untagged frames and assigns them directly to its local native VLAN 20.Cevap
- BSpanning Tree Protocol (STP) automatically bridges the broadcast domains of VLAN 10 and VLAN 20 to preserve network topology convergence upon detecting the mismatch.
- CThe switchport speed/duplex mismatch on the link causes excessive late collisions, forcing untagged frames to flood across all broadcast domains on both switches.
- DThe switches automatically establish an internal Layer 3 Switched Virtual Interface (SVI) proxy route to forward traffic between VLAN 10 and VLAN 20.
Cevap
Switch-Alpha transmits frames originating from VLAN 10 without an 802.1Q header across the trunk, and Switch-Beta accepts these untagged frames and assigns them directly to its local native VLAN 20.
Under the IEEE 802.1Q standard, traffic associated with a trunk port's native VLAN is sent across the link without an Ethernet VLAN tag. When Switch-Alpha (native VLAN 10) transmits untagged frames for VLAN 10, Switch-Beta (native VLAN 20) receives these untagged frames and assigns them to its own native VLAN 20. This causes Layer 2 traffic from VLAN 10 on Switch-Alpha to leak directly into VLAN 20 on Switch-Beta without passing through a Layer 3 device.
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802.1Q Native VLAN Mismatch Traffic Leakage
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