While using a packet analyzer, you notice four additional bytes being added to the packets in
the Company network. Which protocol inserts a four byte tag into the Ethernet frame and
recalculates CRC value?
A.
DTP
B.
VTP
C.
802.1Q
D.
ISL
E.
None of the other alternatives apply
Explanation:
The IEEE 802.1Q protocol can also carry VLAN associations over trunk links. However, this
frame identification method is standardized, allowing VLAN trunks to exist and operate
between equipment from multiple vendors.
In particular, the IEEE 802.1Q standard defines an architecture for VLAN use, services
provided with VLANs, and protocols and algorithms used to provide VLAN services. Like
Cisco ISL, IEEE 802.1Q can be used for VLAN identification with Ethernet trunks. Instead of
encapsulating each frame with a VLAN ID header and trailer, 802.1Q embeds its tagging
information within the Layer 2 frame. This method is referred to as single-tagging or internal
tagging.
802.1Q also introduces the concept of a native VLAN on a trunk. Frames belonging to this
VLAN are not encapsulated with any tagging information. In the event that an end station is
connected to an 802.1Q trunk link, the end station can receive and understand only the
native VLAN frames. This provides a simple way to offer full trunk encapsulation to the
devices that can understand it, while giving normal access stations some inherent
connectivity over the trunk.