Subject: Re: IP packet forward from one POS link into another

From: Leo Huber <[email-masked]>
Date: Wed, 09 Jun 1999 09:47:34 PDT

thx, James.

one more question:

[leo]:
> > could I forward a PPP session into L2TP over POS in
> > the following way?
> >
> > POS in:   UDP2/IP2/PPP2/SDH2 (POS2) -> LAC ->
> > POS out:  UDP2/IP2/PPP2     /L2TP/UDP1/IP1/PPP1/SDH1/ (POS1)->
> >           | forwarded |     |<--added L2TP encapsu-|
> >           |<---PPP2-->|     |lation over POS ----->|
>
[james]:
>Sure.

[leo]:
it means, that the PPP2 is a fully blown PPP session (which
went through the LCP, authentication and NCP phases), not a frame
structure used instead of HDLC to carry payload over POS2?

regards,

leo huber

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---

From: James Carlson <[email-masked]>
Date: Wed, 9 Jun 1999 13:20:39 -0400 (EDT)

> structure used instead of HDLC to carry payload over POS2?

I don't think I understand that question.  PPP uses HDLC as a framing
mechanism.  There's no obvious distinction here between a "full blown
PPP session" and an HDLC link.

Given the diagram above, here's how I understand you might use such a
thing:

	RouterA <--STS-3c--> LAC <--STS-48c--> network <--> LNS

"RouterA" here is running PPP with the LNS.  As far as it can tell, it
is negotiating with the LNS, and all of the data goes straight there,
as if this were a leased point-to-point STS-3c channel.

The LAC wraps this data in L2TP/UDP/IP/PPP and routes it through a
separate network.  That's how the tunnel is established and used
between the LAC and the LNS.

If, on the other hand, you're implying (by "fully blown") that session
PPP2 is handled and regenerated locally, well, yes, that can be done.
Whether and how you do that is strictly outside the standards (though
draft-ietf-pppext-conversion-01.txt will probably be helpful, and
doing so solves some of L2TP's option-related problems).

Of course, I think that all of this probably silly.  MPLS plus either
RSVP or CR-LDP (or both) isn't a great answer, but it's better than
L2TP here -- in terms of overhead, functionality, and likelihood that
any equipment will support the protocol at the data rates you're
talking about.

-- 
James Carlson, Software Architect                   <[email-masked]>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA           42.423N   Fax:  +1 781 372 8090
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp