[173875] in North American Network Operators' Group
Re: [HFC] pooling modems in layer2
daemon@ATHENA.MIT.EDU (charles@thefnf.org)
Tue Aug 12 13:51:31 2014
X-Original-To: nanog@nanog.org
Date: Tue, 12 Aug 2014 12:51:23 -0500
From: charles@thefnf.org
To: nanog@nanog.org
In-Reply-To: <trinity-d9c3a88e-117a-4e72-b5ae-f8abdb225fd4-1407853417989@3capp-mailcom-bs12>
Errors-To: nanog-bounces@nanog.org
On 2014-08-12 09:23, Toney Mareo wrote:
> Hello
>
> I think it's kind of an isp secret but I would be curious how do
> people distribute modems to pools before they would even reach the
> actual IP network so on layer2:
>
> http://dl.packetstormsecurity.net/papers/evaluation/docsis/Service_Distribution.jpg
>
>
> For this I would like to get some clarification because I do not work
> in the telco industry. As I can figure out of the docsis, cablelabs
> documents. The CMTS device is connected to the coax segments through
> fiber. Therefore one could say that the "modem facing" side is a fiber
> optic interface but it's not 1000 Base-FX, not a regular Ethernet over
> fiber. It sends signals through a broad range of frequencies.
Sounds about right to me.
>
> So what I would like to accomplish to provide a different pool of dhcp
> servers, which provides different config file, tod server, router, dns
> etc. infos to the modems but to do all this in Layer2.
>
Why? Do you have a bunch of cable modems and a CMTS? If so, does the
documentation not cover this? Or are you trying to hack your cable
modem/cable provider?
> I don't have hands on experience with CMTS-es but I would think that
> they are able to pool clients by MACs and able to send eg 500 clients
> to DHCP server1 and the other 1500 to DHCP server2 before they would
> even get an IP, so I talking of pure layer2 here!
>
> Let's say if the CMTS device does not support this, what are the other
> options for routing layer2 traffic coming out of the CMTS?
Um. Probably via RADIUS and via VLAN assignment?
If I would
> know more about the device I would say that put a linuxbox after it
> (on the ISP facing nic) and mark the packets going out with
> arptables/ebtables then send them out of different nics to different
> dhcp servers.
Most likely they just use VLANs. This rack of CMTS gear is on port 22 of
the agg switch, vlan 2 and ip helper is set for vlan 2 to the desired
dhcp server (which is most likely an HA floating IP if not a full blown
VIP etc).
