Re: MAE-EAST Moving? from Tysons corner to reston VA.

["Steven M. Bellovin" <smb () research att com>]

In message <87256900.00780D04.00 () d53mta03h boulder ibm com>, trall () almaden ibm.
com writes:
> On 06/16/2000 at 11:10:55 AST, John Fraizer <nanog () EnterZone Net> wrote:
> > If I'm not mistaken, 9000bytes is the max.
>
> I don't understand how ethernets, at the MAC layer, can support frames
> greater than 1500 bytes.  Looking at the MAC frame format, we have:
>
> ethernet DIX V2    DA(16 bits), SA(16 bits), type (16 bits), data
> IEEE 802.3         DA(16 bits), SA(16 bits), length (16 bits), LPDU (802.2)
>
> The traditional way to distinguish between the 2 formats depends on the
> length value (in 802.3) being no greater than 1500, and on the type value
> (in DIX) being greater than 0x05dc (1500 decimal).
>
> Assuming you're still going to allow both formats on the same lan, how does
> it work if the length is greater than 1500?

See http://search.ietf.org/internet-drafts/draft-kaplan-isis-ext-eth-02.txt
for one proposal.

                --Steve Bellovin