mailing list archives
Re: Fwd: Re: DOCSIS 3.0 & PPPoE/L2TP compatibility
From: Scott Helms <khelms () ispalliance net>
Date: Wed, 01 Aug 2012 10:23:26 -0400
We ended up using something like this to separate out the traffic at
layer 2 for each ISP:
Look at section 5.1.2 Multiple ISP L2VPNs
Basically the modems get DHCP & their config from the cable operator but
the CPEs get DHCP (and IP connectivity) from the individual ISPs.
On 8/1/2012 10:17 AM, iptech wrote:
Thanks for the feedback,
yes this is how I understand it also, however I find it strange that
the Cisco platform designated as the future LNS will not accommodate
the DOCSIS 3.0requirements - not much collaboration. There is no
roadmap for introcducing PPTP on the ASR1K that I can see, so i will
not be holding out for one.
I am veering towards using a L2 pw solution, but would be interested
to hear what you have used in-house yourself to accommodate this
change, care to share?
On 7/31/2012 5:46 PM, Scott Helms wrote:
I've actually run into this specific problem and the issue your running
into is that at no time was PPPoE part of the DOCSIS specification. It
was supported on several CMTSs because the Cisco UBR shares much of its
OS with more mainline Cisco routers which support L2TP and a host of
other non-DOCSIS related protocols. It was also widely supported on
some of the earliest CMTSs which were bridges instead of routers (then
you needed a separate box to be the LNS). The real problem isn't a
change in DOCSIS version but that they choose a platform that doesn't
share a code base with a general purpose router. This could have been
happenstance or by design, but I can tell you your chances of getting
PPPoE to work at all on that platform (even for the cable operator) are
not high because the box will not operate as a bridge and there is no
(AFAIK) way to relay the PPP discover packets.
The D3 Arris is either a C4 or a C4C:
On 7/30/2012 8:33 AM, iptech wrote:
We are a small ISP and have a setup in place with the local cable
company for terminating their users via L2TP for Internet access.
However they have just announced to us that they are moving to a
DOCSIS 3.0 compliant setup, and this standard no longer supports PPPoE
via L2TP, and can now only offer PPTP for terminating with us.
We have already begun replacing our Cisco 7206VXR LNS devices with
Cisco ASR 1Ks and as you will be aware the older 7206 can do both L2TP
and PPTP, whereas the ASR1k can do only L2TP. I do not have any
experience in the cable arena, but from what I have read in the DOCSIS
standards, each version has maintained backwards compatibility,
therefore I am very surprised our CableCo has claimed they cannot do
The CMTS they are currently using is a Cisco, and now they are moving
to a new ARRIS CMTS. I have not been able to find any information on
this device and what it can do or not. With the ASR1K marked as the
natural upgrade path for LNS functions, therefore I cannot believe
that it is not fully compatible with DOCSIS 3.0.
From what I can tell the only way to accommodate the new CMTS PPTP
connections will be to terminate them on the legacy 7206VXR, which at
the end of the day is a backwards step. I would greatly appreciate if
anyone can give me any pointers and/or suggestions on this matter, so
I can understand it and move it forward.
FYI: The driver for the CMTS upgrades is to offer higher bandwidth
access speeds 15mb-20mb.
Vice President of Technology