Subject: I-D ACTION:draft-sadler-pppext-disc-01.txt

From: [email-masked]
Date: Tue, 04 Jun 2002 07:43:42 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: Neighbor Discovery via PPP
	Author(s)	: J. Sadler, B. Mack-Crane
	Filename	: draft-sadler-pppext-disc-01.txt
	Pages		: 7
	Date		: 03-Jun-02
	
Work has been progressing in the Common Control and Measurement
Protocol (CCAMP) working group on the application of MPLS technology
to non-packet switching networks.  Development of the Generalized
MPLS (GMPLS) signaling draft [1] has allowed for Optical, SONET/SDH,
and spatial switching systems to be controlled using IP protocols.
In a GMPLS network, the path that a TDM connection will use is
developed using constraint based routing.  The developed route
utilizes TDM link state information announced via OSPF or IS-IS by
other nodes in the network.  However, a node cannot advertise the
existence of a link without first identifying the remote node
connected to the link and the capabilities of the neighboring node.
In a packet network, this function would typically be accomplished
using OSPF or IS-IS Hello messages repeated every 10 or so seconds.
However, the TDM link cannot transmit similar messages because the
port terminating the link cannot be shared between a TDM service
user and the OSPF/IS-IS termination function.

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From: James Carlson <[email-masked]>
Date: Tue, 4 Jun 2002 08:37:21 -0400

> 6.1.4 Misconnection failure modes
> 
>    Because successful LCP negotiation is dependent on a full-duplex
>    link existing between two neighboring nodes, a misconnection will
>    not allow LCP to complete successfully.  As a result, any support
>    for identifying a misconnection must be done via an LCP option.
>    Given that a misconnection may occur for any supported Interface,
>    the exchange of Interface Names provides the best information for
>    debugging a misconnection.

I'm failing to see the justification of a new LCP option here (or
6.1.3).  What the document seems to be saying above is also true of
any NCP that runs over PPP: one doesn't want to have a simple
misconfiguration result in a bad link being established.  That doesn't
mean that all NCPs should be negotiated in LCP.

If I understand this draft correctly, it proposes having LCP
negotiate, go to Opened state, and then somehow, at some point,
release the port so that some other non-PPP service ('TDM') can use
the port.  This raises several significant problems: the document does
not describe exactly when and how this hand-off occurs, it does not
describe what happens if the peer attempts to restart LCP (unless
physical end-to-end signaling is always required, and that's not a
requirement of PPP), and it does not describe how this feature
interacts with the existing suite of PPP features (e.g.,
Authentication, CHAP rechallenge, LQM, MP, CCP, ECP, and basic LCP
Echo-Request/Response).

An alternative -- one that would require no changes to PPP at all --
would be an agreement by the peers to use PAP or EAP to exchange
identities, and to place the link identity in the "peer name" field.
Since this proposal is an identification mechanism, it seems logical
to use the existing identification mechanisms to support it.

However, this proposal also appears to be using PPP as though it were
a one-shot exchange, which is not the case.  This is troubling in
terms of the feature support outlined above.  It seems to me that a
new protocol -- say, "one time identity exchange protocol" -- would be
preferable to redefinition of all of the PPP subprotocols to fit in
this context.

There are other issues with the draft (e.g., the session ID doesn't
appear to be necessary, since the peers themselves already know over
which port they're communicating -- there can be only one session on
any given peer-to-peer connection), but I think those can wait until
the fundamental questions are addressed.

-- 
James Carlson, Solaris Networking         <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677

---

From: Bernard Aboba <[email-masked]>
Date: Tue, 4 Jun 2002 06:21:27 -0700 (PDT)

> to use the existing identification mechanisms to support it.

I think that this would work fine. In particular, there is nothing in RFC
2284 that prohibits sending an EAP-Request/Identity, receiving an
EAP-Response/Identity, and then sending an EAP-Success to end the
exchange.

---

From: James Carlson <[email-masked]>
Date: Tue, 4 Jun 2002 10:27:59 -0400

> EAP-Response/Identity, and then sending an EAP-Success to end the

Nor is there anything that actually says what (if any) internal
structure might exist in the "Identity" value.  It's all based on
prior agreement between the peers.