An administrator issues the `show interfaces trunk` command on Switch-A while troubleshooting inter-switch connectivity to Switch-B. The command output confirms that interface GigabitEthernet1/0/1 is actively trunking using 802.1Q encapsulation. However, syslog messages periodically display `%CDP-4-NATIVE_VLAN_MISMATCH` notifications because Switch-A is configured with native VLAN 30 while Switch-B uses native VLAN 1. Which two statements accurately describe how frames are handled across this link? (Select two.)
- Frames generated by hosts in VLAN 30 on Switch-A are transmitted across the trunk link without an 802.1Q header tag.Answer
- Untagged frames arriving at Switch-B from Switch-A will be placed into VLAN 1, resulting in cross-VLAN traffic leakage.Answer
- CSwitch-A automatically forces interface GigabitEthernet1/0/1 into an err-disabled state upon detecting the VLAN mismatch.
- DEnabling Spanning Tree PortFast on GigabitEthernet1/0/1 suppresses the native VLAN mismatch logs while preserving trunk functionality.
Answer
Frames originating from VLAN 30 on Switch-A are transmitted without an 802.1Q tag, and Switch-B associates incoming untagged frames with its own native VLAN (VLAN 1).
Under IEEE 802.1Q specifications, traffic matching the native VLAN of the transmitting switch interface is sent without an 802.1Q header. Because Switch-A has a native VLAN of 30, it sends VLAN 30 frames untagged. Upon receiving untagged frames, Switch-B associates them with its own native VLAN (VLAN 1). This results in unexpected cross-VLAN communication between VLAN 30 on Switch-A and VLAN 1 on Switch-B.
Step-by-Step Solution
Key Concept
802.1Q Native VLAN Tagging Mechanics and Mismatch Behavior