Some advice on IPv6 planning and ARIN request, please

Mark Andrews marka at
Tue Jul 11 03:09:39 CST 2017

In message <596349CF.9000709 at>, Thomas Bellman writes:
> Hash: SHA1
> On 2017-07-08 23:00, Radu-Adrian Feurdean wrote:
> > On Sat, Jul 8, 2017, at 19:13, Mel Beckman wrote:
> >> That open atmosphere was by design. It's why IPv6 uses 128-bit addresses,
> > 
> > That's for hosts. When you care more about subnets, it's shortened to 64
> > bits.
> Indeed.  Especielly if you do hierarchical delegation within your
> organization, you will often have sparse allocations at several
> levels.  A /48 for an organization might seem like reasonably lots
> with 65536 subnets, but if that organization in turn delegates to
> departments, and they have more than 16 departments, each department
> might only get a /56 (256 subnets).

If I had 32 departments and were wanting to give them equal sized
allocations then I'd give them a /53 each which is 2064 subnets
each.  It isn't that hard to do 8 delegations in the reverse tree
for each of the 32 departments.  Delegation on nibble boundaries
is for convience and nothing else.

Or you could start with a /56 each and reserve the next 7 /56s for
each department to grow into.

>  Try to delegate that one step
> further, and you can't do any reasonable allocation strategy, but
> have to allocate subnet by subnet.

Of which the only downside is that it is harder to do internal
firewalls between departments or if you want to do cost recovery
of external traffic to departments.  The DHCPv6 servers also need
to learn where to get additional subnets from to fulfill PD requests.

Remember a site can have more than one /48.  Thats just the recommended
starting point.

> I managed to get a full /52 from our host university, but they
> initially wanted to give us only a /56.  Of course, they can only
> give out a few /52:s; other departments will have less structured
> address plans than us.
> - -- 
> Thomas Bellman,  National Supercomputer Centre,  Linköping Univ., Sweden
> "Life IS pain, highness.  Anyone who tells   !  bellman @ nsc . liu . se
>  differently is selling something."          !  Make Love -- Nicht Wahr!
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at

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