How to manage Static IPs to customers

Blake Hudson blake at
Fri May 8 21:26:29 UTC 2020

16 connectors per DCAM2 times 6 cards is 96 DS service groups in a 
chassis. At ~1.2 Gbps per connector (using 32 SC-QAM DOCSIS 3.0 
channels) that's ~ 100gigabits per chassis. Quite a bit above my scale ;- )

The E6k can also do DOCSIS 3.1, which we use today, though I'm not sure 
what the capacity limit is per DCAM/SG/connector when both SQ-QAM and 
OFDM are used in combination.


On 5/8/2020 4:13 PM, Luke Guillory wrote:
> E6K using gen 1 DCAMs can do about 32 service groups give or take, not 
> that hard to get to a point with splits where you want to go past 
> those numbers. Gen 2 DCAMs double that by going to 16 connectors 
> compared to 8. cBR8 is less than the E6K.
> The point of node splits is to lower customers per SG, you can’t just 
> split and stay on the same chassis if you’re at capacity on slots.
> If you take the Comcast approach and start pushing fiber deeper in 
> order to remove actives your node counts sky rocket. All the whole 
> they’re lowering counts on SGs as well.
> Even us little guys or working on lowering customers per SG, they have 
> to be moved somewhere which would be another chassis if you’re out of 
> free connectors on like cards.
> Like
> /Sent from my iPhone/
>> On May 8, 2020, at 4:02 PM, Blake Hudson <blake at> wrote:
> Aaron, I was thinking something similar. I've never once had a node
> split require moving a customer to a different CMTS. Even the very old
> and (relatively) low capacity 7200 VXR could serve several nodes per
> line card and supported several line cards per chassis. Newer cBR8, E6k,
> and the like can serve many many times more customers across dozens of
> nodes. Every L3 CMTS I've worked on uses something akin to ip unnumbered
> so as long as the customer stays on the same CMTS, their IP address will
> continue to work regardless of what interface or line card their
> connection terminates on.
> On 5/8/2020 2:34 PM, Aaron Gould wrote:
>> We have a provisioning system (promptlink) that we use to map cable 
>> modems
>> to their static ip addresses.  The provisioning system has a gui 
>> front end
>> and it sits on linux and also acts as a dhcp server, etc.  This is 
>> the same
>> ip address that we use for cable-helper (like ip-helper on a cmts 
>> bundle ip
>> interface) to forward dhcp requests from cable modem cpe, via the 
>> cmts, and
>> unicasted to promptlink and then the static ip address reservation within
>> the promptlink is sent back to the cpe
>> This all continues to work, even during node splits, as long as we don't
>> move that cm cpe to a different cmts... which would rarely happen 
>> since it's
>> across town to get to our other RF environment served be a different cmts
>> using a different static ip subnet... since we don't do L2 via cmts's in
>> order to stitch back that ip into a more globally located static 
>> subnet...
>> again, we don't do that.  If the customers moves locations, into a 
>> different
>> cmts area, that would be required to give back the single static /32 
>> ip and
>> get a different on.  Unless they were a multi-static customer buying 
>> like a
>> /29... in which case we have no problem moving that /29 subnet off 
>> that cmts
>> and onto another one.  That's easy.
>> We do however have more centrally located subnets for some of our single
>> static ip customers in FTTH... but not CMTS docsis.
>> -Aaron
>> -----Original Message-----
>> From: NANOG [mailto:nanog-bounces at] On Behalf Of Javier 
>> Gutierrez
>> Guerra
>> Sent: Thursday, May 7, 2020 3:50 PM
>> To: nanog at
>> Subject: How to manage Static IPs to customers
>> Hi there,
>> Just wanted to reach out and get an idea how is people managing customers
>> with static Ips, more specifically on Docsis networks where the customer
>> could be moved between cmts's when a node is split
>> Thanks in advance for all responses,
>> Javier Gutierrez Guerra

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