[146951] in North American Network Operators' Group
Re: IPv6 prefixes longer then /64: are they possible in DOCSIS
daemon@ATHENA.MIT.EDU (Dmitry Cherkasov)
Tue Nov 29 07:01:08 2011
In-Reply-To: <CAF95533.1B70F7%john_brzozowski@cable.comcast.com>
Date: Tue, 29 Nov 2011 13:59:53 +0200
From: Dmitry Cherkasov <doctorchd@gmail.com>
To: NANOG <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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@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. =C2=A0A randomized algorithm could also be =
used.
> Another consideration is what happens after IPv6 is used for addressing
> cable modems. =C2=A0What happens when you want to address CPE or CPE rout=
ers?
> You are right back to /64 or shorter depending on the type of device bein=
g
> provisioned.
>
> FWIW - we have found that there are distinct benefits to using IPv6 beyon=
d
> the amount of addresses that are available. =C2=A0The use of /64 is tight=
ly
> 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@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 =C2=A0SLAAC is not us=
ed
>>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
>>
>
