[ppml] [address-policy-wg] Those pesky ULAs again

[Thomas Narten]

> sounds like a great idea for all of ipv6 allocation.  what is the
> difference ula or pi/pa?

Here's my take.

ULAs are not intended to be publically routed by ISPs. While some may
attempt to get ISPs to route them, ISPs will have clear documentation
saying they are not intended to be used that way, and they are free to
filter them. And in fact they SHOULD be filtered. (I'd say MUST, but
since that is not enforceable...) 

We have ULAs already. What is missing is centralized ULAs. I've had
enough conversations with people that want to use ULAs - but simply
aren't satisfied with probalistic uniqueness. They want something more
meaningful, like a signed contract that that can pay some fee for and
get some assurance that no one else is going to get that address. This
sort of thing makes business people happy. People do worry about
collisions and the impact that would have.

ULAs are intended to be much more easy to obtain than PI space,
because PI space is intended to be publically routed. PI space, on the
other hand, is not useful if it is not publically routed (generally
speaking). Poeple obtaining PI space are very much assuming it will be
publically routed.

ULA space is useful even if not publically routed (and is intended for
uses that do not require public routability). E.g., it can be used to
number infrastructure devices, with assurance those addresses will not
need to change the way public addresses might.

Is ULA space the same as PI? Only if you want to give everybody and
their brother PI space and don't care about what that does to the
routing tables. I don't believe we can (or should) do that.

And keep in mind, in IPv6 devices can have multiple addresses
simultaneously. So it is quite possible to have ULA-C addresses in
addition to public addresses. So having ULA-C addresses does not imply
that those addresses have to be used for communicating with off-site
destinations.

Thomas