Fwd: Re: DOCSIS 3.0 & PPPoE/L2TP compatibility

Scott Helms khelms at ispalliance.net
Wed Aug 1 09:23:26 CDT 2012


We ended up using something like this to separate out the traffic at 
layer 2 for each ISP:

http://www.cablelabs.com/cablemodem/downloads/specs/CM-SP-L2VPN-I03-061222.pdf

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:
> 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.
>>
>> The D3 Arris is either a C4 or a C4C:
>> http://www.arrisi.com/products/product.asp?id=3
>>
>> 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.
>>>
>>> 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.
>>>
>>> Thank you.
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>


-- 
Scott Helms
Vice President of Technology
ZCorum
(678) 507-5000
--------------------------------
http://twitter.com/kscotthelms
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