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. 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@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