Subject: RE: AW: PPP Frames on tunnel

From: "Shriver, John" <[email-masked]>
Date: Tue, 1 Aug 2000 09:00:34 -0700

I think that the address and control fields remain present on the tunnel
because L2TP inherited the "very dumb LAC" model from the PPTP PAC.  In
PPTP, the PAC never participated in PPP at the LCP layer or higher, it was a
modem bank that understood HDLC framing (sync or async) and nothing more.
This is still one of the two modes of L2TP.

L2TP is not an ideal standard, it was a political compromise between Cisco
(L2F) and Microsoft (PPTP).  This was one of Microsoft's "design wins" in
the merged protocol.

I know that the IETF doesn't like to think that their protocols are designed
on a political basis, but it happens, but normally in less explicit ways.
It happened in L2TP, and it happend (back-room) in PPP.

(I'll admit that I haven't been following the full thread, and will sign off
this discussion now.)

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From: Bill Palter <[email-masked]>
Date: Tue, 01 Aug 2000 09:12:32 -0700

> (L2F) and Microsoft (PPTP).  This was one of Microsoft's "design wins" in

  L2F also had the FF03 field present, but for different reasons....So it
wasn't so much a compromise as something that was the same that no one saw 
the need to change. When the desire to change it came up, we had already 
shown interoperability at 2 bakeoffs so we din't want to change it that late 
in the game (of course, as it turned out there would have been plenty of time
to change it)...

--
Bill Palter ([email-masked])

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From: "P. Rakity" <[email-masked]>
Date: Wed, 2 Aug 2000 02:04:22 -0700 (PDT)

Folks,

At one of the early bake-off's we suggested changing the frame format to
not have the FF 03.  This change could not be done

a) because the rfc was moments from being published 
b) there we exisiting working implementations.

The reality was b) was certainly true and a) took another year.

regards,

Philip

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From: "W. Mark Townsley" <[email-masked]>
Date: Wed, 02 Aug 2000 08:37:38 -0400

> The reality was b) was certainly true and a) took another year.

These were certainly two strong arguments. Two that we all remember
well. I am definitely not challenging that. 

The other reasons that I stated at the beginning of this thread were
some that were sited at the time *in addition* to these. Nothing more.

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From: "W. Mark Townsley" <[email-masked]>
Date: Tue, 01 Aug 2000 17:36:38 -0400

> This is still one of the two modes of L2TP.

Yes. Not removing FF03 allowed the LAC to be a dumb bridge for HDLC, a
significant design constraint at the time. The question now is whether
we should force non-HDLC PPP LACs to be 'smart' and make the tunneled
frames look like they came from an HDLC device regardless. 

> (L2F) and Microsoft (PPTP).  This was one of Microsoft's "design wins" in

The fact that both L2F and PPTP came up with the same result was
certainly signficant in the design (or merging) of L2TP.