IPv6 Addressing Help

William Herrin herrin-nanog at dirtside.com
Fri Aug 14 15:52:42 CDT 2009

On Fri, Aug 14, 2009 at 2:40 PM, Jeroen Massar<jeroen at unfix.org> wrote:
> William Herrin wrote:
> [..]
>> I'm not aware of any way of dynamically assigning an IPv6 subnet to a
>> customer that's as well automated as IPv4 /32 dynamic assignment to a
>> DSL router with an RFC1918 NATed interior, but that may just be my
>> ignorance since I haven't needed to research it.
> DHCP-PD (prefix delegation)

Hi Jeroen,

Cool. So we'll have $100 CPE which uses it in a relatively idiot-proof
manner sometime between now and eternity.

>> Static IP customer: /60
> ARIN defines a /56 minimum. That is the reason that ISPs get a /32.
> RIPE defines a /48 at the moment.

ARIN "defines" a /64 minimum customer assignment and suggests /56.
They go on to say that, "RIRs/NIRs are not concerned about which
address size an LIR/ISP actually assigns."

See ARIN NRPM  https://www.arin.net/policy/nrpm.html#six54

>> I recommend /60 as the customer default where most folks suggest /56
>> or /48. The IPv6 use profile looks a heck of a lot like the IPv4 use
>> profile and /60 is 16 subnets. How many of your customers find a
>> reason to use more than 3 IPv4 subnets, including their RFC1918 ones?
>> Relatively few.
> Think Future. And why bother with that anyway. If you as an ISP needs
> more address space just ring RIPE/ARIN/APNIC and ask for more, they will
> happily give it to you.

The future looks a lot like the past but with more blinking lights.
Seriously, I'm pretty nuts when it comes to networking. My basement is
AS11875, multihomed with about 35mbps of bandwidth. If I can't imagine
how *I* would use more than 16 subnets then it's a safe bet that many
years will pass before Joe random DSL customer wants to.

The world won't end, even if you assign every customer a /48. But why
be so grossly wasteful *before* anyone has demonstrated a practical
use for doing so?

> I guess you ran the numbers on how to run out of IPv6 address space?

IIRC, RIPE allocated a /19 to France Telecom. Doesn't take more than a
few hundred thousand allocations like that one to wipe out the IPv6
address space.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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