IPv6 fc00::/7 ??? Unique local addresses

Sun Oct 24 14:04:42 UTC 2010

On Oct 24, 2010, at 6:48 AM, Leo Bicknell wrote:

> In a message written on Sat, Oct 23, 2010 at 05:23:14PM -0700, Owen DeLong wrote:
>> On Oct 23, 2010, at 8:03 AM, Carlos Martinez-Cagnazzo wrote:
>>> On Fri, Oct 22, 2010 at 11:38 AM, Leo Bicknell <bicknell at ufp.org> wrote:
>>>> There are some folks (like me) who advocate a DHCPv6 that can convey
>>>> a default gateway AND the ability to turn off RA's entirely.  That
>>>> is make it work like IPv4.
>>>> 
>>> I'd also love to turn off stateless autoconfig altogether and not be coerced
>>> to assign /64s to single LANs, which I am becoming convinced that it was a
>>> poor decision on the IETFs part.
>>> 
>> Nah... The /64 thing is fine. If they hadn't done that, we likely would have only
>> a 64-bit address space total.  64-bit lans with 64-bit routing identifiers are
>> fine.
> 
> I think the 64-bit boundry is fine (from a DHCP perspective).  I
> do think if we're going to update the DHCP spec it should support
> a netmask option, just because leaving it out is short sighted to
> the future, but I would use it with /64's today.
> 
My understanding was DHCPv6 did support prefixes other than /64.

>> There really is no need for anything smaller than /64.  What, exactly, do you
>> think you gain from a smaller netmask?
> 
> There is a slippery slope here, if users make do with smaller
> providers may give out smaller blocks, and so on.
> 
Yeah, that could be worse than neutral. Still there's no gain to smaller
than /64, only loss...

> That said, if a provider does hand out a /64, I would very much
> like technology to make 16 bits of subnet + 48 bits of host, with
> EUI-48 used directly for autoconf as an option.  Particularly when
> we talk about 6rd and other things that use a lot of space this
> option would be huge.  Users would still get 16 bits of subnet, and
> host space so big they could never fill it.
> 
I think that ship has pretty well sailed, but, it might be a good future
workaround if providers start doing stupid pet tricks like assigning
single /64s to end customers.

Owen