comcast ipv6 PTR

Tue Oct 15 16:48:32 UTC 2013

Michael Thomas <mike at mtcc.com> writes:
> On 10/15/2013 08:35 AM, TJ wrote:
>>>
>>> My cable company assigns me a different prefix every time the modem
>>> reboots, about once a month, and I think that's pretty typical.
>>>
>> Really?
>> I think my IPv6 address form Comcast has changed (maybe) twice in the last
>> 18 months, and I think it was only once.
>>
>
> There's an entire universe within ietf who thinks that seamless
> renumbering is
> a Big Deal. We're obviously not completely there -- especially within
> residential --
> but any path forward should not count on the stability of
> prefixes. Anywhere.

Agreed.

We will allocate semi-static prefixes, but have decided to do strict
aggregation of retail subscriber prefixes on the BNGs. This means that
the allocations will be perceived as static by most users, but there are
no guarantees. We will renumber if the users move between BNGs,
regardless of reason.  Including moving DSLAMs/OLTs.

Having said that: Renumbering is not going to be seemless, even for
simple home networks.  The last time I changed my home prefix, I
completely forgot that I had put the old one into a cups access list.
Took me a while to figure out why I couldn't make the printer work a
month or so later...

Typical static entries being added over time are:
 - DNS glue
 - access lists, both in your network and in other networks
 - interface config on devices where you don't want SLAAC or DHCPv6
 - server application configuration (you do want your mail server to use
   a specific source address and not just choose one, right?)
 + everything I forgot

No, renumbering is not going to be seemless.  Yes, a smarter person
could automate everything I list above, but we all know that's not going
to happen.

Bjørn