How to manage Static IPs to customers

Blake Hudson blake at
Fri May 8 21:01:13 UTC 2020

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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