What is required for a LAN switch to support 802.1q Q-in-Q encapsulation?

A.
Support less than 1500 MTU

B.
Support 1504 MTU or higher

C.
Support 1522 layer 3 IP and IPX packet

D.
Support 1547 MTU only

Explanation:
The default system MTU for traffic on Catalyst switches is 1500 bytes. Because the 802.1Q tunneling (Q-in-Q) feature increases the frame size by 4 bytes when the
extra tag is added, you must configure all switches in the service-provider network to be able to process maximum frames by increasing the switch system MTU
size to at least 1504 bytes.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_13_ea1/config uration/guide/swtunnel.html