Subject: Do we want a new L2TP Header?

From: "W. Mark Townsley" <[email-masked]>
Date: Mon, 21 May 2001 11:59:55 -0700

L2TP currently has two classes of headers. (1) Those defined in RFC2661,
and (2) those defined in draft-ietf-l2tpext-l2tphc-03.txt. Within each
class, we have more than one header we have to recognize, based on the
bits set in the beginning of the header or signaling that occurred at
session establishment (particularly for the case of l2tphc). 

Even in light of this complexity, we enjoy exceptional interoperability
among so many independent implementations that I lost count a long time
ago. Also, like many protocols, the variability defined in the original
specification has begun to converge into a more static subset of fields
that we most often see in L2TP deployments today. Rather than letting
nature continue to take its course for better or worse and require all
new implementations to continue to include code for what are
increasingly rare expectations, I would like to get a sense of the group
as to whether we should entertain definition of a new, fixed, header
with L2TP. Many of you have approached me offline about this, so I
thought that bringing the idea to the list would be appropriate.

An easy transition to a new header would be aided by the signaling that
we all support. We would simply advertise support for the new header at
tunnel and session establishment, much like we do for l2tphc. The hope
would be that, one day, all implementations would converge on this
header and that our hardware, ASICs, etc. only have to support this
rather than than the various headers we have today that are identified
on a per-packet basis. 

In the past, I have rejected a major change like this, citing that any
improvement in the header would not be worth disrupting our existing
interoperable codebases. However, with the open-heart surgery that is
ongoing in RFC2661 to separate the L2TP tunneling plane from PPP and
more and more people pushing L2TP processing down into microcode and
ASICs (essentially requiring a rewrite of our data paths anyway), I
wonder now is the time to go ahead and apply what we have learned over
the past 5 years with hope of paving a way for the next 5 years. 

I have a set of ideas that have culminated over the past couple of years
that I would be happy to post to the list to initiate discussion, but
only if there is interest and consensus that definition of a new header
for L2TP is a Good Thing to do.

Comments appreciated,

- Mark

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From: Elwin Eliazer <[email-masked]>
Date: Mon, 21 May 2001 17:11:54 -0700 (PDT)

Having a fixed size header would definitely help
data-path processing were transit packets enter
or leave an L2TP tunnel.
I would like to hear more discussions on this.

regards,
Elwin.

--- "W. Mark Townsley" <[email-masked]> wrote:
> and (2) those defined in
> draft-ietf-l2tpext-l2tphc-03.txt. Within each

=====
-------
Elwin Stelzer Eliazer
Corona Networks
-------

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From: Ron da Silva <[email-masked]>
Date: Tue, 22 May 2001 14:17:23 -0400

On Mon, May 21, 2001 at 11:59:55AM -0700, W. Mark Townsley wrote:

<snip>

> ...I would like to get a sense of the group

sounds like the right approach.

-ron

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ron da Silva                          [email-masked]
Network Architect                    703.265.4548
America Online, Inc.
A wholly owned subsidiary of AOL Time Warner Inc.

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From: "Suhail Nanji" <[email-masked]>
Date: Wed, 23 May 2001 09:22:31 -0700

I think a discussion on the list about a new fixed header is worthwhile.

Suhail

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf
> Of Ron da Silva
> Sent: Tuesday, May 22, 2001 11:17 AM
> To: W. Mark Townsley
> Cc: [email-masked]
> Subject: Re: Do we want a new L2TP Header?
> 
>