Fwd: Re: DOCSIS 3.0 & PPPoE/L2TP compatibility

iptech iptech at northrock.bm
Wed Aug 1 09:17:09 CDT 2012


Hi Scott,

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?

Thanks

On 7/31/2012 5:46 PM, Scott Helms wrote:
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> 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.
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> The D3 Arris is either a C4 or a C4C:
> http://www.arrisi.com/products/product.asp?id=3
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> On 7/30/2012 8:33 AM, iptech wrote:
>> Hi,
>>
>> 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
>> PPPoE/L2TP anymore.
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>> 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.
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>> 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.
>>
>> Thank you.
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