2.2. Unique Local IPv6 Addresses
...
Because a ULA and a global site prefix are both /48 length, an
administrator can choose to use the same subnetting (and host
addressing) plan for both prefixes.
The RIRs are moving away from a rigid /48 policy. It would be safer
to start this sentence with "When" instead of "Because".
And on the same topic...
2.4. Network Level Design Considerations
I suggest adding a bullet at the end of this section along these
lines:
o It is possible that as registry policies evolve, a small site
may experience an increase in prefix length when renumbering,
e.g. from /48 to /56. For this reason, the best practice is
number subnets compactly rather than sparsely, and to
use low-order bits as much as possible when numbering subnets.
In other words, even if a /48 is allocated, act as though
only a /56 is available. Clearly, this advice does not apply
to large sites and enterprises that have an intrinsic need
for a /48 prefix.
2.4.2. Address Space Conservation
Despite the large IPv6 address space which enables easier subnetting,
it still is important to ensure an efficient use of this resource.
Some addressing schemes, while facilitating aggregation and
management, could lead to significant numbers of addresses being
unused. Address conservation requirements are less stringent in IPv6
but they should still be observed.
The proposed HD [8] value for IPv6 is 0.94 compared to the current
value of 0.96 for IPv4. Note that for IPv6 HD is calculated for
sites (i.e. on a basis of /48), instead of based on addresses like
with IPv4.
Perhaps it would be wiser to make the parenthesis
(e.g. on a basis of /48)
Thanks for adding the ISP case. Some comments...
5.2.1.2. IPv6 addressing schema requirements from the ISP perspective
of the Service Provider
From ISP perspective the following basic requirements could be
identified:
o The IPv6 address allocation schema must be able to realize a
maximal aggregation of all IPv6 address delegations to customers
into the /20 of the Service Provider. Only this /20 will be
routed and injected from the Service Provider into the global
routing table (DFZ). This strong aggregation keeps the routing
tables of the DFZ small and eases filtering and access control
very much. (Note: A strong aggregation e.g. on POP or LER basis
limits as well the numbers of customer routes that are visible
within the ISP network.)
I'm quite concerned by this. Basically, why? Are we really expecting
ISPs to have so many customer sites that they can't simply flat-route
internally? Yes, that may be slightly less attractive for an MPLS
based ISP rather than for one using IP routing, but it has horrible
consequences because of the way it constrains address assignment.
5.2.1.3. IPv6 addressing schema requirements from the Network Access
provider perspective of the Service Provider
As already done for the LIR and the ISP roles of the SP it is also
necessary to identify requirements that come from its Network Access
Provider role. Some of the basic requirements are:
o The IPv6 addressing schema of the SP must be flexible enough to
adapt changes that are injected from the customer side. This
covers changes that are based on the raising IPv6 address needs of
the customer as well as changes that come from topological
modifications (e.g. when the customer moves from one point of
network attachment (POP) to another).
I don't understand "changes that are injected from the customer side."
Does this mean injected by a routing protocol? What sort of flexibility
do you mean? And when a customer changes POP, well, see my previous
comment. That should just be a routing change.