Subject: Re: L2TP charter

From: Danny McPherson <[email-masked]>
Date: Thu, 27 Jul 2000 00:12:29 -0600

Because X is an array of protocols (Layer 3 or lower), and ISPs absolutely 
want to converge these services (e.g. ATM & Frame Relay) onto IP core 
networks.  Trivial L2TP extensions provide an elegant mechanism to do this, 
without the baggage of heavier IP tunneling protocols.

-danny

> I'd like to register skepticism on extending L2TP to tunnel other
> things.  Primarily, I'd resist with vigor any attempt to make
> "L2TP standard compliant" depend on support for anything but PPP.
> Dunno if the proponents really intend that, but the proposed
> charter language makes me a little paranoid.
> 
> Secondarily, I'd really like to hear why X needs to be carried over
> L2TP, rather than over whatever X is carried over today.

---

From: James Carlson <[email-masked]>
Date: Thu, 27 Jul 2000 06:41:43 -0400 (EDT)

> without the baggage of heavier IP tunneling protocols.

Layer 3 or lower?  Could I interpret this to mean SNA over L2TP or
DECNet over L2TP?

I don't understand your objection to the "heavier" baggage of other IP
tunneling protocols.  L2TP has a default encapsulation of UDP-GRE and
thus is heavier than IP-GRE.  There's some precedent for using IP-GRE
encapsulation to carry non-IP payloads across IP networks.  Do we need
another?

You're right that ISPs do want to converge services, but I don't think
L2TP is the right mechanism for that convergence.  MPLS has much lower
overhead, behaves in a hop-by-hop manner familiar to ATM and Frame
Relay operators and is already quite compatible with those protocols
and defines interworking standards, and (very much unlike L2TP) is
already supported in core routers.  MPLS is much more suited to this
task.

I suggest that L2TP stick to its roots in providing tunneling support
for dial-up network access protocols only.  This should be explicitly
listed in its charter, along with examples of such protocols -- PPP
and SLIP.

(If someone has a need to carry ARAP across a network, I'd waver and
say that the charter is still too broad.  ARAP inexplicably requires
MNP for reliability and might be more suitably tunneled over TCP.)

-- 
James Carlson                                  <[email-masked]>
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp