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Re: MAE-EAST Moving? from Tysons corner to reston VA.
From: "Steven M. Bellovin" <smb () research att com>
Date: Fri, 16 Jun 2000 18:04:42 -0400


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





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