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

Brzozowski, John John_Brzozowski at Cable.Comcast.com
Mon Nov 28 22:30:57 UTC 2011


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
>





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