nanog mailing list archives

Re: at&t business ipv6


From: Randy Bush <randy () psg com>
Date: Thu, 21 Jun 2018 09:19:43 -0700

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.

aha!  makes sense.

i'll settle for dynamic.  if i need static internally, i can always do
nat66 :)/2

i do not want to play how hard can we make ipv6 deployment; just want to
enable it on a five-segment office lan.

but i am beginning to see that there may be a reason i am having
problems getting past an account rep.

randy


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