[pptp-server] Using PoPToP in conjunction with L2TP and a PPP concentrator

[Tim Wilfong]

I know fairly well how L2TP works, but haven't been able to get enough
info on PPTP to know that protocol as well (can't seem to find the RFC
anywhere.) I assume PPTP works similarly to L2TP, though. With L2TP, a
PPP session is encapsulated inside an L2TP tunnel -- thus, at the
termination point of the tunnel, once you strip away the L2TP
encapsulation, you now have a PPP session, which you can either
terminate, or send through another tunnel to be terminated elsewhere.
My understanding of PPTP is that it works similarly, but, again, I
might be mistaken.

Do you know where I might find the RFC for PPTP? (All pointers to it
on the PoPToP site are bad.)

-Tim


-----Original Message-----
From: Trevor Benson [mailto:Tbenson at associatedbp.com]
Sent: Tuesday, April 24, 2001 12:01 PM
To: 'Tim Wilfong'
Subject: RE: [pptp-server] Using PoPToP in conjunction with L2TP and a
PPP concentrator


Tim,

   I may be completely wrong on this. But it sounds like your talking about
taking a 'tunnel' and then moving the ppp connection elsewhere.  The tunnel
is being created by the ppp connection, and then pptp tunneled inside it. So
in essence I think you would be adding another ppp, not rerouting it.  Since
ppp is required for the tunnel to initiate, I don't think you could just
reroute to a concentrator, since the tunnel you are referring to has to be
created prior to routing on internal LAN.  

   Like I said, I might have misread your question, or not have the full
grasp of PoPToP, but I think that's accurate for what your asking.


Thanks,
Trevor

 -----Original Message-----
From: 	Tim Wilfong [mailto:tim.wilfong at aubeta.net] 
Sent:	Monday, April 23, 2001 7:13 PM
To:	'pptp-server at lists.schulte.org'
Subject:	[pptp-server] Using PoPToP in conjunction with L2TP and a
PPP concentrator

Has anyone tried using PoPToP to terminate the PPP session somewhere other
than
the server that that PoPToP is running on. i.e. It is feasible to take the
PPP
session and send it out an L2TP tunnel to an PPP concentrator, so that the
user 
that is using PPTP to "dial-in" looks just like users dialing into that
dial-up 
server. Has anyone tried experimenting with this? It seeems that PoPToP
already
sends the PPP sessions to a seperate PPP daemon to handle the termination of
the
PPP session, so it would be a matter of modifying an L2TP (or PPPoE, for
that 
matter) client to take these sessions and tunnel them to a PPP concentrator.

If this could be set up, then a Linux server running PoPToP could be used as
a tunnel switcher to allow legacy PPTP clients to access an L2TP-based VPN 
server, thus allowing easier migration to an L2TP-based VPN solution. (Of
course, 
there are many security implications from this, but let's ignore those for
now.)

-- Tim Wilfong
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