Re: [v6ops] ULA precedence [Thoughts about wider operational input]

[Brian E Carpenter <[e-mail]>]

On 25-Apr-22 12:16, Lorenzo Colitti wrote:
> On Mon, Apr 25, 2022 at 2:28 AM Erik Auerswald <[e-mail] <mailto:[e-mail]>> wrote:
> 
>       "Since ULAs are defined to have a /48 site prefix, an implementation
>        might choose to add such a row automatically on a machine with
>        a ULA."
> 
>     The result is that only the local ULA prefix, i.e., exactly the
>     local IPv6 addresses, are preferred over IPv4 (and IPv6 GUA).
>     This should be exactly what is needed to use ULA addresses inside
>     an organization, or for a lab.
>     [...]
>     Implementing the non-normative suggestion from Section 10.6 of RFC
>     6724 would in all likelihood result in making ULA usable for local
>     tests and even first steps in deploying IPv6.  ULA addresses would
>     only be used locally.  Existing IPv4 based Internet access would not
>     be impaired by adding IPv6 ULA.
> 
> 
> That does seem like it might make ULA more useful, yes.
> 
> Additionally, maybe we could clarify that the longest-prefix match rule 
does not apply to ULAs outside the same /48? I think that would fix the issue observed by +Ted Lemon <mailto:[e-mail]> in home networks: https://datatracker.ietf.org/meeting/113/materials/slides-113-6man-source-address-selection-for-foreign-ulas-00 <https://datatracker.ietf.org/meeting/113/materials/slides-113-6man-source-address-selection-for-foreign-ulas-00> .

When two networks each with its own ULA prefix are intentionally merged, longest match would be the right thing, wouldn't it? (Assuming that the split DNSs are also merged, and of course internal routing.) In that case there is no "foreign" ULA prefix.

>     In order to keep IPv6 deployment similar to IPv4, IPv6 NAT could be
>     considered.  To make this work as intended, the address selection
>     policy table could be adjusted to contain the local ULA prefix
>     with precedence greater or equal to GUA and the same label as GUA.
> 
> 
> This seems like it would encourage the use of IPv6 NAT. I think there is reasonably strong consensus within the IETF that that is not the right way to go, because it pushes problems on to application developers. This adds costs for NAT traversal software development and maintenance, and requires devices to implement NAT keepalives, increasing battery usage.

That may be the IETF's consensus, but there is a very large fraction of the enterprise network operations community that strongly disagrees, and in fact regards this as a red line issue. It isn't even clear that they'd accept NPTv6 as an alternative to NAPT66. If this is indeed the only way to get IPv6 inside enterprises, what is the right thing for the IETF to do?

       Brian