[arin-ppml] Draft Policy ARIN-2020-3: IPv6 Nano-allocations

David Farmer farmer at umn.edu
Sun Apr 19 04:43:16 EDT 2020

On Sun, Apr 19, 2020 at 12:21 AM Fernando Frediani <fhfrediani at gmail.com>

> On 19/04/2020 01:38, David Farmer wrote:
> I support this policy as written, as I said previously, I recommend a
> couple of changes, but I won't repeat the details of those changes here.
> Regarding the current discussion of /48 assignments to
> residential customers, that is the architecture as defined by the IETF, and
> ARIN policy MUST NOT create situations where its necessary or that
> incentivizes ISPs to make assignments longer than /48. Further, this policy
> is at least minimally consistent with the IPv6 architecture, and /48 IPv6
> assignments, when considering a 3X-Small ISP, with a /24 of IPv4 and a /40
> of IPv6, both address families will reasonably support 250 or fewer
> customers.
> Can you please quote exactly where IETF defines that way ?
> RFC6177 in its abstract says: "*RFC 3177 argued that in IPv6, end sites
> should be assigned /48 blocks in most cases.  The Regional Internet
> Registries (RIRs) adopted that recommendation in 2002, but began
> reconsidering the policy in 2005. This document obsoletes the RFC 3177
> recommendations on the  assignment of IPv6 address space to end sites. The
> exact choice of how much address space to assign end sites is an issue for
> the operational community.  The IETF's role in this case is limited to
> providing guidance on IPv6 architectural and operational considerations.*"
> ...
> "*This document reviews the architectural and operational considerations
> of end site assignments as well as the motivations behind the original
> recommendations in RFC 3177. Moreover, this document clarifies that a
> one-size-fits-all recommendation of /48 is not nuanced enough for the broad
> range of end sites and is no longer recommended as a single default.*"
> The number of customers and the size of IPv6 customer assignments actually
> deployed in reality are outside the scope and control of ARIN, the other
> RIRs, and even the IETF. It is solely in the scope and control of the ISP
> deploying a network. Furthermore, RFC 6177 recognizes longer end-site
> assignments between /48 and /64 could be reasonable.
> Recognizes as an exception and it clearly states that is not the
> recommendation anymore, talks about all the issues and why it was reviewed
> and mentions that if someone justify can get it, so as an exception.
No, it doesn't eliminate /48 as a recommendation, it clarifies that /48 is
not a requirement of the IPv6 architecture, it eliminates /48 as the
default, eliminating the idea of /48 as a one-size-fits-all. However, /48
effectively remains as the maximum recommended end-site assignment, with
/64 as the minimum, reaffirming that "in practice, that means at least one
/64, and in most cases significantly more." So, even after RFC 6177, /48
still plays an important part in the IPv6 architecture, it just more
nuanced than it was in RFC 3177.

So, if you want to assign /56s or /60s, or /48s for that matter, you are in
compliance with RFC 6177 and ARIN policy, at least in my opinion.

> Given all above I cannot agree and have the same view that /48 to
> residential customers indistinctly is a normal thing and that RIRs should
> necessarily adapt to allow ISPs to make these assignments the way is being
> suggested in this discussion.
> Regards
Even with RFC 6177, /48 is still relevant in the context of, and
instructive to, ARIN policy, in helping to determine the size of
allocations ARIN makes. In that, if ARIN policy assumed only /56
assignments, let's say, then it would be impossible for ISPs to make /48
assignments, as they wouldn't have enough space to do so. Therefore, ARIN
policy needs to assume /48 for assignments, allowing ISPs to make the
assignments sizes they wish to, between /48 and /64. Nothing in ARIN policy
requires /48 assignments by ISPs, it simply allows up to /48 without
additional justification.

There are reasons to assign /48s even to residential customers, Owen
articulates them well, but nothing in ARIN policy requires this, however,
ARIN policy needs to allow for /48 assignments as an option. In the case of
this policy, relating to /40 allocations for 3X-Small ISPs, if you were to
make /48 assignments you can still make a sufficiently large number of them
for the expected customer base of 3X-Small ISPs, and you can make even more
if you make /56 or /60 assignments. However, if instead of a /40
allocation, we made it a /44 allocation, then you could only make 16 /48
assignments, and this is not a reasonable number of customer assignments
even for a 3X-Small ISP.


David Farmer               Email:farmer at umn.edu
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE        Phone: 612-626-0815
Minneapolis, MN 55414-3029   Cell: 612-812-9952
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