12 years ago
A normative question:
AS we all know, ethernet has a max packet size of 1514 bytes:
14 bytes header (dst + src + len/type), plus 1500 bytes data.
For 802.1Q tagging, the spec was changed to allow a max packet size
of 1518 bytes: 1514 bytes, plus 4 bytes for the .1Q type/tag/prio fields.
For QinQ tagging, has the base spec been changed again,
now to a size of 1522 bytes, to allow for the double .1Q fields?
Are there any plans to go beyond this?
I'm kind of surprized because some hardware does have the packet size
hard-coded in, and while a careful study was done when the first
packet size change was made, changing this again and again may cause
trouble and I'd like to understand the rationale behind this.
(and no, jumbograms isn't the answer - suppose you have hardware which
is capable of 9kB packets, the same hardware may not be capable to carry
9kB+2bytes needed for .1Q, or 9kB+4bytes for QinQ protocols)