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

Mon Nov 28 22:39:13 UTC 2011

I mentioned this in an earlier reply.  CM vs CPE vs CPE router are all
different use cases.  From a CPE or CPE router point of view SLAAC will
likely not be used to provisioned devices, stateful DHCPv6 is required.
As such Vista/7 machines that are directly connected to cable modems will
receive an IPv6 address and configuration options via stateful DHCPv6.
The same now applies to OSX Lion.

I do agree that many host implementations have been built around /64
assumptions and departures from the same at this time will seemingly
introduce more problems that benefits.

John

On 11/28/11 5:00 PM, "Steven Bellovin" <smb at cs.columbia.edu> wrote:

>
>On Nov 28, 2011, at 4:51 52PM, Owen DeLong wrote:
>
>> 
>> On Nov 28, 2011, at 7:29 AM, Ray Soucy wrote:
>> 
>>> 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).
>>> 
>> 
>> Technically, absent buggy {firm,soft}ware, you can use a /127. There's
>>no
>> actual benefit to doing anything longer than a /64 unless you have
>> buggy *ware (ping pong attacks only work against buggy *ware),
>> and there can be some advantages to choosing addresses other than
>> ::1 and ::2 in some cases. If you're letting outside packets target your
>> point-to-point links, you have bigger problems than neighbor table
>> attacks. If not, then the neighbor table attack is a bit of a
>>red-herring.
>> 
>
>The context is DOCSIS, i.e., primarily residential cable modem users, and
>the cable company ISPs do not want to spend time on customer care and
>hand-holding.  How are most v6 machines configured by default?  That is,
>what did Microsoft do for Windows Vista and Windows 7?  If they're set for
>stateless autoconfig, I strongly suspect that most ISPs will want to stick
>with that and hand out /64s to each network.  (That's apart from the
>larger
>question of why they should want to do anything else...)
>
>
>		--Steve Bellovin, https://www.cs.columbia.edu/~smb
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