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

Mon Nov 28 15:29:11 UTC 2011

It's a good practice to reserve a 64-bit prefix for each network.
That's a good general rule.  For point to point or link networks you
can use something as small as a 126-bit prefix (we do).

When it comes to implementation, though, it's not as simple as a yes
or no answer.

The actual use of 64-bit prefixes is not something I would currently
recommend for large-scale deployments due to the denial of service
attack vector it opens up (neighbor table exhaustion).

Not using 64-bit prefixes tosses SLAAC out the window; but for many
networks SLAAC may not be desirable anyway due to the lack of control
it presents.

Once vendors come out with routers that are able to protect against
neighbor table exhaustion, moving to a 64-bit prefix (which you
hopefully reserved) will allow you to be more flexible in what
addressing methods are used.

On Mon, Nov 28, 2011 at 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
>
>

-- 
Ray Soucy

Epic Communications Specialist

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