IPv6 Default Allocation - What size allocation are you giving out

Thu Oct 9 07:02:09 UTC 2014

On Wed, Oct 8, 2014 at 10:48 PM, James R Cutler
<james.cutler at consultant.com> wrote:
> On Oct 8, 2014, at 9:18 PM, Erik Sundberg <ESundberg at nitelusa.com> wrote:
>> I am planning out our IPv6 deployment right now and I am trying to figure out our default allocation for customer LAN blocks. So what is everyone giving for a default LAN allocation for IPv6 Customers.  I guess the idea of handing a customer /56 (256 /64s) or  a /48 (65,536 /64s) just makes me cringe at the waste. Especially when you know 90% of customers will never have more than 2 or 3 subnets. As I see it the customer can always ask for more IPv6 Space.
>>
>> /64
>> /60
>> /56
>> /48

Hi Erik,

You're asking the right question and you understand the
divisible-by-four rule for prefix delegation, which is good. The
answer I recommend is:

1. Nothing smaller than /56 unless you know enough about the situation
to be sure /56 is unnecessary. In particular, never provide a /64 to a
customer... delegate nothing between /61 and /123, ever. You'll just
be making mess that you have to clean up later when it turns out they
needed 3 LANs after all.

2. Suggest /56 for residential and /48 for business customers as
default, didn't ask for something else sizes.

3. /48 for anyone who makes the effort to ask, including residential
customers. 99% won't ask and won't care any time in the foreseeable
future.

4. Referral to ARIN for anyone who requests more than a /48. If they
have a good reason for needing more than 65,000 LANs that reason is
likely good enough to justify a direct ARIN assignment. If they don't
have a good reason, the experience will teach them that without
needing to get them mad at you.

> Selection of a default prefix is easy.  Here are the steps.
>
> 4. Keeping in mind
>
>         4.1 Prefixes longer than somewhere around /48 to /56 may be excluded from the global routing table

4.1a Prefix cutouts of any size (including /48) from inside your /32
or larger block may be excluded from the global routing table. Folks
who are multihomed and thus need to advertise their own block with BGP
should be referred to ARIN for a direct assignment. Folks who aren't
multihomed, well, until given evidence otherwise I claim there are no
single-homed entities who will use 65,000 LANs, let alone more.

>         4.2 Your customers want working Internet connections
>         4.3 You want income at a minimum of ongoing expense
>
>    make a sensible business decision.

IPv6 is large but not infinite. No need to be conservative, but
profligate consumption is equally without merit.

Regards,
Bill Herrin

-- 
William Herrin ................ herrin at dirtside.com  bill at herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
May I solve your unusual networking challenges?