Wireshark-dev: Re: [Wireshark-dev] Minsize of 802.1Q Frames
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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Thu, 16 Oct 2008 10:47:58 -0700

On Oct 16, 2008, at 10:08 AM, Joerg Mayer wrote:
What is the minimum frame size of a tagged Ethernet frame (802.1Q)? 64 or 68? 

64.  See section 3.5 of

	http://standards.ieee.org/getieee802/download/802.3-2005_section1.pdf

(I obviously left out the preamble and SFD, but included the FCS).
I think the minimum frame size originally came from a requirement that an Ethernet frame had to span the entire Ethernet segment by the time the last part of the frame was transmitted; that means that the total content of the frame, including the Ethernet header, any 802.1Q headers, the payload, and the FCS, has to be >= the minimum size, so the more 802.1Q headers you have, the fewer bytes of payload you need to get to the minimum frame size.