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

Victor Kuarsingh victor.kuarsingh at gmail.com
Tue Nov 29 07:17:35 CST 2011

Dmitry et al,

I found Jeff's following comments to be quite insightful for general



As for using 127s on P2P links....

He discussed reasoning behind using /64s, concerns related to "waste", ND
exploits and
other points as noted in RFC6164. - directed


Victor K

On 11-11-29 7:58 AM, "Dmitry Cherkasov" <doctorchd at gmail.com> wrote:

>Thanks to everybody participating in the discussion.
>I try to summarize.
>1) There is no any obvious benefit of using longer prefixes then /64
>in DOCSIS networks yet there are no definite objections to use them
>except that it violates best practices and may lead to some problems
>in the future
>2) DHCPv6 server can use any algorithm to generate interface ID part
>of the address, and EUI-64 may be just one of them that can be useful
>for keeping correspondence between MAC and IPv6 addresses. Yet if we
>use EUI-64 we definitely need to use /64 prefix
>3) Using /64 networks possesses potential security threat related to
>neighbor tables overflow. This is wide IPv6 problem and not related to
>DOCSIS only
>There were also notes about address usage on link networks. Though
>this was out of the scope of original question it is agreed that using
>/64 is not reasonable here. BTW, RFC6164 (Using 127-Bit IPv6 Prefixes
>on Inter-Router Links) can be mentioned here.
>Dmitry Cherkasov
>2011/11/29 Dmitry Cherkasov <doctorchd at gmail.com>:
>> Tore,
>> To comply with this policy we delegate at least /64 to end-users
>> gateways. But this policy does not cover the network between WAN
>> interfaces of CPE and ISP access gateway.
>> Dmitry Cherkasov
>> 2011/11/29 Tore Anderson <tore.anderson at redpill-linpro.com>:
>>> * Dmitry Cherkasov
>>>> 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.
>>> I am not familiar with DOCSIS networks, but I thought I'd note that in
>>> order to comply with the RIPE policies, you must assign at least a /64
>>> or shorter to each end user:
>>> http://www.ripe.net/ripe/docs/ripe-523#assignment_size
>>> --
>>> Tore Anderson
>>> Redpill Linpro AS - http://www.redpill-linpro.com

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