Re: [IPv6] Second Working Group Last Call for <draft-ietf-6man-rfc6724-update>

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

Jeremy,

On 11-Apr-24 23:43, Jeremy Duncan wrote:
> Lorenzo-
> 
> This is misleading at best and incorrect at worst:
> 
> “Preferring non-local ULA over IPv4 is incorrect because IPv4 implies global reachability, and ULA does not offer global reachability”

This is correct if you add in the assumption that all RFC1918 deployments are behind a NAT44. So I think it's true in practice if not in theory.

With one complication - IPv4 link-local addresses.

     Brian

> 
> IPv4 with RFC 1918 is not globally reachable as is ULA. When networks are comprised with private and non-routable subnets they may include both IPv6 ULA and IPv4 1918 addresses for the explicit purpose to not be routable on the internet.
> 
> -Jeremy
> 
> *From:*ipv6 <[e-mail]> *On Behalf Of *Lorenzo Colitti
> *Sent:* Wednesday, April 10, 2024 11:30 PM
> *To:* Ted Lemon <[e-mail]>
> *Cc:* Bob Hinden <[e-mail]>; IPv6 List <[e-mail]>
> *Subject:* Re: [IPv6] Second Working Group Last Call for <draft-ietf-6man-rfc6724-update>
> 
> On Thu, Apr 11, 2024 at 1:04 AM Ted Lemon <[e-mail] <mailto:[e-mail]>> wrote:
> 
>     I continue to think that section 3,  "Operational Issues Regarding Preference for IPv4 addresses over ULAs," should make the new proposed ULA behavior mandatory rather than optional. I don't see a downside to making it mandatory. Hosts will come into compliance when they can; older implementations will not implement this new behavior, but I don't see any point in perpetuating that.
> 
> Absolutely agree. This document should not proceed without that MUST. Preferring non-local ULA over IPv4 is incorrect because IPv4 implies global reachability, and ULA does not offer global reachability. So publishing this document without the MUST is harmful: an implementation that does not implement the SHOULD will cause regressions and break use cases that work today.
> 
> Also, MUST allows us to make ULA more useful than it is today. It is *desirable* to be able to publish non-local ULAs and have hosts know what is local and what is not. As a simple example: once all hosts implement the MUST, it will be safe to publish local ULAs in the global DNS, because hosts won't try to use them unless they are local.
> 
> 
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