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Cisco 640-878 Exam
Which three statements about VLAN implementation in a Layer 2 switch environment are true? (Choose three.)
A. The Cisco IOS switchport access vlan interface configuration command is used to configure the native VLAN on the switch port.
B. 802.1AD supports VLAN overlap.
C. VLANs can span across multiple switches.
D. 802.1Q encapsulation is used to identify different VLANs on a trunk port.
E. Inter-VLAN routing is performed between VLAN tunnel ports.
Correct Answer: BCD
Explanation/Reference:
Explanation: Explanation/Reference:
IEEE 802.1ad[note 1] is an Ethernet networking standard informally known as IEEE 802.1QinQ and is an amendment to IEEE standard IEEE 802.1Q-1998. The technique is also known as provider bridging, Stacked VLANs or simply QinQ or Q-in-Q.
The original 802.1Q specification allows a single VLAN header to be inserted into an Ethernet frame. QinQ allows multiple VLAN headers to be inserted into a single frame, an essential capability for implementing Metro Ethernet network topologies. Just as QinQ extends 802.1Q, QinQ itself is extended by other Metro Ethernet protocols.[specify] In a multiple VLAN header context, out of convenience the term “VLAN tag” or just “tag” for short is often used in place of “802.1Q VLAN header”. QinQ allows multiple VLAN tags in an Ethernet frame; together these tags constitute a tag stack. When used in the context of an Ethernet frame, a QinQ frame is a frame that has 2 VLAN 802.1Q headers (double-tagged).
There is a mild confusion regarding the naming because the 802.1ad standard was grown out of the 802.1QinQ protocol (which was developed based the trademarked method 802.1Q, with capital “Q” as a distinction instead of the 802.1q as the standardised protocol) which originally used 0x9100 as ethernet type instead of 0x88a8. While the network industry usually mix the naming the proper, standardised name is 802.1ad which sometimes gets appended by the other alternative names mentioned above; the plain “802.1QinQ” name usually refers to the old standard which is now considered obsolete
