Which two of these are characteristics of the 802.1Q protocol? (Choose two)

Cisco Certified Network Associate Exam

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Which two of these are characteristics of the 802.1Q protocol? (Choose two)



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A. B. C. D. E.


The correct answers are A and B.

802.1Q is a standard protocol used in virtual LAN (VLAN) configurations on Ethernet networks. It adds a tag to the Ethernet frame, allowing multiple VLANs to be carried over a single physical link.

The characteristics of the 802.1Q protocol are as follows:

A. it is a layer 2 messaging protocol which maintains VLAN configurations across the network: 802.1Q is a layer 2 protocol, which means it operates at the data link layer of the OSI model. It is used to maintain VLAN configurations across the network by tagging Ethernet frames with VLAN identifiers (VIDs). This allows the switches to forward frames to the appropriate VLANs based on the VLAN IDs.

B. it includes an 8-bit field which specifies the priority of a frame: 802.1Q includes a priority field that is used to prioritize frames in a network. This field is an 8-bit field that is added to the Ethernet frame header. It is used to ensure that certain types of traffic (such as voice or video) receive higher priority than other types of traffic (such as file transfers).

C. it is used exclusively for tagging VLAN frames and does not address network reconvergence following switched network topology changes: This statement is incorrect. 802.1Q is used for tagging VLAN frames, but it also provides a mechanism for addressing network reconvergence following switched network topology changes. When a switch detects a change in the network topology, it sends out a special type of frame called a topology change notification (TCN). This frame contains information about the change and is propagated throughout the network so that other switches can update their forwarding tables accordingly.

D. it modifies the 802.3 frame header, and thus requires that the FCS be recomputed: This statement is partially correct. 802.1Q does modify the 802.3 frame header by adding a 4-byte VLAN tag, but it does not require that the frame check sequence (FCS) be recomputed. The FCS is a field in the Ethernet frame that is used to check for errors in the transmission of the frame. It is recalculated after the VLAN tag is added, but this does not require recomputation of the entire FCS.

E. it is a trunking protocol capable of carrying untagged frames: This statement is partially correct. 802.1Q is a trunking protocol, which means it is used to carry VLAN traffic between switches over a single physical link. However, it cannot carry untagged frames. All frames carried over an 802.1Q trunk must be tagged with a VLAN ID.