Which option is the minimum frame size for an 802.1Q frame?
A. 64 bytes
B. 68 bytes
C. 1518 bytes
D. 1522 bytes
Cisco implementation says 68 bytes
The 802.1Q tag is 4 bytes. Therefore, the resulting Ethernet frame can be as large as 1522 bytes. The minimum size of the Ethernet frame with 802.1Q tagging is 68 bytes.
IEEE implementation says 64 bytes
I believe 64 bytes is enough to detect the collision, no matter with/without Tag.
Thanks for the reply,
My question is does cisco realy follows minimum required frame size with the tag as 68?
I should answer 64 or 68?
Thank you @Mark Malone
But if you see my question there I have attached a 64 bytes frame with tag,
That is actually taken from cisco switch cat 3550.
your understanding is correct.
the minimum size is 64 bytes because an 802.1Q tagged frame is STILL a standard ethernet frame.
This was more put in evidence when 802.1Q was compared with Cisco proprietary ISL. (30 bytes overhead 26 bytes header and 4 byte CRC, an ISL frame is NOT a standard ethernet frame but carries an ethernet frame in its payload using a tunnel encapsulation).
ISL does not support multiple Vlan tagging (like it is used in QinQ or other forms like provider backbone bridging ).
So this question was easier to answer many years ago when both 802.1Q and ISL were studied and compared.
Note: compliments for you questions they are becoming a challenge to answer.
Hope to help