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

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

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

Explanation: IEEE 802.1Q is the networking standard that supports Virtual LANs (VLANs) on an Ethernet network. It is a protocol that allows VLANs to communicate with one another using a router. 802.1Q trunks support tagged and untagged frames.

If a switch receives untagged frames on a trunk port, it believes that frame is a part of the native VLAN. Also, frames from a native VLAN are not tagged when exiting the switch via a trunk port.

The 802.1q frame format is same as 802.3. The only change is the addition of 4 bytes fields. That additional header includes a field with which to identify the VLAN number. Because inserting this header changes the frame, 802.1Q encapsulation forces a recalculation of the original FCS field in the Ethernet trailer.

Note: Frame Check Sequence (FCS) is a four-octet field used to verify that the frame was received without loss or error. FCS is based on the contents of the entire frame.

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