200-301 Question 194
Single answerA network engineer is tasked with configuring VLANs on a switch to segment traffic. The switch is connected to another switch via a trunk link. The engineer decides to use 802.1Q for VLAN tagging. Which of the following statements about 802.1Q is correct?
- A
802.1Q adds a 4-byte VLAN tag to the Ethernet frame while preserving the original frame structure.
- B
802.1Q is only used for tagging traffic on access ports.
- C
802.1Q uses a proprietary protocol for VLAN tagging, only supported by Cisco devices.
- D
802.1Q removes the Ethernet frame's original header and replaces it with a VLAN tag.
Show answer and explanation
Correct answer: A
Explanation
The IEEE 802.1Q standard is widely used for VLAN tagging on trunk links, allowing multiple VLANs to be identified and transported over a single physical link. It adds a 4-byte VLAN tag to the Ethernet frame, which includes the VLAN ID and other fields, while preserving the original frame structure. This makes it versatile and interoperable across devices from different vendors.
- A. Correct.
802.1Q adds a 4-byte VLAN tag to Ethernet frames, which includes fields such as VLAN ID and priority. The original frame is preserved except for adding the tag, making this the correct statement.
- B. Incorrect.
802.1Q is used on trunk links to tag traffic from multiple VLANs, not on access ports, which typically carry untagged traffic.
- C. Incorrect.
802.1Q is an open standard for VLAN tagging, not a proprietary protocol. It is supported by multiple vendors, not just Cisco.
- D. Incorrect.
802.1Q does not remove the original Ethernet frame header. It modifies the frame by inserting a VLAN tag between the Source MAC and EtherType fields.