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

Tue Nov 29 17:21:13 UTC 2011

On Nov 29, 2011, at 4:58 AM, Dmitry Cherkasov 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
> 
99% of which can be easily mitigated by ACLs, especially in the context
you are describing.

> 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.
> 

I don't agree that using /64 on link networks is not reasonable. It's perfectly
fine and there is no policy against it. There are risks (buggy router code
having ping pong attack exposure, ND table overflow attacks if not
protected by ACL), but, otherwise, there's nothing wrong with it.

Owen

> 
> 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