IPv6 prefixes longer then /64: are they possible in DOCSIS networks?

Tue Nov 29 11:59:53 UTC 2011

John,

I am determining technical requirements to IPv6 provisioning system
for DOCSIS networks and I am deciding if it is worth to restrict user
to use not less then /64 networks on cable interface. It is obvious
that no true economy of IP addresses can be achieved with increasing
prefix length above 64 bits.

As for using EUI-64, unlike random or sequential generation it
provides predictable results that may be desired, e.g. for tracking
some device migration between different networks.

Dmitry Cherkasov

2011/11/29 Brzozowski, John <John_Brzozowski at cable.comcast.com>:
> Dmitry,
>
>
> You could consider the use of prefixes longer than the /64 on CMTS
> interfaces, however, it is not clear to me why this would be done.
> Further, most DHCPv6 implementations do not require that the generated
> IPv6 address be eui-64 based.  A randomized algorithm could also be used.
> Another consideration is what happens after IPv6 is used for addressing
> cable modems.  What happens when you want to address CPE or CPE routers?
> You are right back to /64 or shorter depending on the type of device being
> provisioned.
>
> FWIW - we have found that there are distinct benefits to using IPv6 beyond
> the amount of addresses that are available.  The use of /64 is tightly
> coupled with these benefits.
>
> Can you elaborate as to why one would want to or need to use prefixes
> longer than /64?
>
> John
>
> On 11/28/11 6:37 AM, "Dmitry Cherkasov" <doctorchd at gmail.com> wrote:
>
>>Hello everybody,
>>
>>It is commonly agreed that /64 is maximal length for LANs because if
>>we use longer prefix we introduce conflict with stateless address
>>autoconfiguration (SLAAC) based on EUI-64 spec. But  SLAAC is not used
>>in DOCSIS networks. So there seems to be no objections to use smaller
>>networks per cable interfaces of CMTS. I was not able to find any
>>recommendations anywhere including Cable Labs specs for using
>>prefixes not greater then /64 in DOCSIS networks. Some tech from ISP
>>assumed that DHCPv6 server may generate interface ID part of IPv6
>>address similarly to EUI-64 so MAC address of the device can easily be
>>obtained from its IPv6 address, but this does not seem like convincing
>>argument. What do you think?
>>
>>
>>Dmitry Cherkasov
>>
>