What is the reason given for the ping behavior in the trunk example?

What is the reason given for the ping behavior in the trunk example?

• A. Packets are tagged on the trunk
• B. Packets are untagged between the two switches
• C. Traffic is blocked by a firewall
• D. VLAN 111 is native on the other side

Answer: (B)

On a 802.1Q trunk, traffic for most VLANs is tagged as it crosses the link, while traffic for the native VLAN is sent untagged. If the ping behavior shown in the trunk example comes from frames that are untagged as they traverse between the switches, that means the traffic is being carried as native VLAN frames rather than as tagged VLAN 111 traffic. As a result, the frames don’t carry the VLAN identification across the trunk, so they aren’t associated with the correct VLAN on the far end, and the ping doesn’t reach the intended device in VLAN 111. Tagged traffic would pass for the proper VLAN, while untagged frames explain the observed behavior.

On a 802.1Q trunk, traffic for most VLANs is tagged as it crosses the link, while traffic for the native VLAN is sent untagged. If the ping behavior shown in the trunk example comes from frames that are untagged as they traverse between the switches, that means the traffic is being carried as native VLAN frames rather than as tagged VLAN 111 traffic. As a result, the frames don’t carry the VLAN identification across the trunk, so they aren’t associated with the correct VLAN on the far end, and the ping doesn’t reach the intended device in VLAN 111. Tagged traffic would pass for the proper VLAN, while untagged frames explain the observed behavior.