oops, I replied about this to the previous thread, didn't realize it had split.
https://www.ripe.net/ripe/mail/archives/db-wg/2021-July/007118.html

-Cynthia

On Wed, Jul 21, 2021 at 12:08 AM Job Snijders via db-wg <db-wg@ripe.net> wrote:
Hello db group,

On Tue, Jul 20, 2021 at 10:11:46PM +0200, Edward Shryane via db-wg wrote:
> According to the implementation plan:
> https://www.ripe.net/ripe/mail/archives/db-wg/2021-March/006876.html
>
> if these ranges are not marked as "available" or "reserved" in an
> RIR's delegated stats, then it will be skipped, and I didn't find
> 192.88.99.0/24 in any RIR's delegated stats.
>
> (To Ronald and the list) Should we add other sources of bogon prefixes
> (e.g. RFC 3068) to the implementation?

RFC 3068 was obsoleted by RFC 7526, a document that 'deprecates'
192.88.99.0/24. The whole thing is here: https://www.rfc-editor.org/rfc/rfc7526.html

Unfortuntaly, RFC 7526 is not entirely clear on what 'deprecation' means
in context of for example the 'Forwardable' and 'Globally Reachable'
colums of the "IANA IPv4 Special-Purpose Address Registry" table at:
https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml

The goal of RFC 7526 seems to be to discourage further growth of the
6to4 anycast network, but doesn't specify what should happen with
existing 6to4 deployments (other than needing to be 'reviewed').

I personally probably wouldn't object to the removal of
'route: 192.88.99.0/24' objects from the RIPE-NONAUTH database, but some
quick testing on my personal Internet connection shows 6to4 instances
still ping and forwarding paths to 192.88.99.1 still exist. I know of
some corporate ISPs that block 192.88.99.0/24, but clearly not every
operator filters. What does this mean?

Perhaps the topic of what to do IPv4/IPv6 transition prefixes in the
RIPE-NONAUTH DB should be brought up in the RIPE IPv6 WG?

Kind regards,

Job
(speaking as db-wg enthusiast)