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CCNA & ICND2 Question:

Which encapsulation uses a native VLAN?

A) ISL

B) 802.1q

C) Both ISL and 802.1q


Answer: B
802.1Q is the IEEE standard for tagging frames on a trunk and supports upto 4096 VLANs. In 802.1Q, the trunking device inserts a four-byte tag into the original frame and recomputes the Frame Check Sequence (FCS) before sending the frame over the trunk link. At the receiving end, the tag is removed and the frame is forwarded to the assigned VLAN. 802.1Q does not tag frames on the native VLAN. It tags all other frames transmitted and received on the trunk. While configuring 802.1 trunk, you must make sure that the same native VLAN is configured on both sides of the trunk. IEEE 802.1Q defines a single instance of spanning tree running on the native VLAN for all VLANs in the network which is called Mono Spanning Tree (MST). This lacks the flexibility and load balancing capability of PVST avialable with ISL. However, PVST+ offers the capability to retain multiple Spanning Tree topologies with 802.1Q trunking.

To your success,
David Bombal
CCIE #11023, CCSI, CCDP, CCIP, CCNP, CCSP, CCVP
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