CCNA R&S Exam Prep Question of the Week

CCNAMainQOWWhich of the following are characteristics of the 802.1Q protocol? (Choose two.)

A. It is used exclusively for tagging VLAN frames and does not address network convergence following switched network topology changes.
B. It includes an 8-bit field, which specifies the priority of a frame.
C. It modifies the 802.3 frame header and thus requires that the FCS be recomputed.
D. It is a Layer 2 messaging protocol that maintains VLAN configurations across networks.
E. It is a trunking protocol capable of carrying untagged frames.

 

Answer: C and E.

Answer A does not take into account that 802.1Q also has a priority field that is used to carry Class of Service (COS) marking for Quality of Service (QoS). 802.1Q is a tag that is inserted between the source address field and the type or length field in the Ethernet header, therefore the FCS has to be recalculated. Also, the support of the native VLAN with untagged frames within 802.1Q allows for Spanning Tree frames to be sent across the trunk.

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