at&t business ipv6

Thu Jun 21 16:07:48 UTC 2018

Randy Bush wrote on 21/06/2018 16:35:
> anyone been to this movie and care to divulge the plot?

Yes, one particular plotline which can explain why docsis systems do 
this is that standard residential customers are provisioned using giant 
broadcast domains directly on the cable, with DHCP config.  Obviously 
it's more complicated because it's docsis, but lemme handwave and say 
that this is the gist of it.  Because you're dealing with giant 
broadcast domains, you assign IP address blocks to individual CMTSs and 
your customers are assigned out of those ranges.

Assigning ipv6 in this context is really simple: it's part of the 
baseline DOCSIS3.0 standard and is supported incredibly well by all 
parts of the network.

Static addresses don't fit into this paradigm because you if you 
configure your static customers from a single broadcast domain, then 
they are glued to a particular CMTS and can't be moved from that CMTS 
unless you renumber them.

This doesn't work in practice because if you want to grow your network, 
you probably want to be able to move around chunks of your cable network 
from one CMTS to another in order to balance out your traffic.  Or you 
might want to split a bunch of cable nodes from one CMTS to multiple, 
according as your traffic outgrew the capabilities of a single CMTS (a 
node in this context is a small chunk of a cable network).

One way of getting around this mess is to backhaul all your static 
customer interfaces using mpls l2vpn PWHE up to a L3 box which just 
handles static IP addresses.  You configure the customer's static 
default gateway IP address on an interface on this head-end router, and 
the customer's cable modem will have a virtual connection directly to 
that interface.  The thing is, this virtual interface termination system 
might or might not be tied into the entire ipv6 provisioning system.  If 
it isn't, you're SoL.  So even if dirt-cheap residential customers can 
get ipv6 very easily, it's different by virtue of the fact that you're 
using static IP addresses, because they're a headache for cable operators.

Nick