In D50415#1150645, @p.mousavizadeh_protonmail.com wrote:

The ip6.auto_linklocal is enabled by default, and it could create link-local scope violations without any explicit admin configuration.

but:

1. the bridge will be inet6 ifdisabled on boot by default, so it shouldn't have any link-local addresses unless the admin explicitly enabled inet6 on the bridge, in which case they should expect this
2. even if the ifdisabled flag is removed, bridge will automatically remove link-local addresses from interfaces added to the bridge to prevent scope violation; this is controlled by allow_llz_overlap and predates the recent member_ifaddrs change

so the only way this should be possible, unless i'm missing something here, is for the admin to enable inet6 on the bridge and change the default value of allow_llz_overlap.

This panics with a KMSAN violation in the sys/netinet/carp:unicast_v6 test. I'm still digging into that but I don't think it's a problem with this patch itself, rather I think it's an existing problem that's being revealed.

In D50415#1151177, @ivy wrote:

In D50415#1150645, @p.mousavizadeh_protonmail.com wrote:

The ip6.auto_linklocal is enabled by default, and it could create link-local scope violations without any explicit admin configuration.

but:

1. the bridge will be inet6 ifdisabled on boot by default, so it shouldn't have any link-local addresses unless the admin explicitly enabled inet6 on the bridge, in which case they should expect this

It's important to note that most people who use IPv6 have the ipv6_activate_all_interfaces="YES" setting enabled.
I am not sure why IPv6 is not activated by default. I always have IPv6 enabled on all of my interfaces.

In D50415#1151928, @p.mousavizadeh_protonmail.com wrote:

It's important to note that most people who use IPv6 have the ipv6_activate_all_interfaces="YES" setting enabled.

that's true; i never use this myself but i expect there are a lot of people who do. but, this will still be “fixed” by the default setting of allow_llz_overlap, right? (“fixed” in the sense that the bridge will call in6_detach and remove all the IP addresses, preventing any scope violation.)

I am not sure why IPv6 is not activated by default.

personally i don't like IP addresses (including link-local addresses) randomly appearing on interfaces without explicitly enabling that. i believe this is different to how other OSs work by default (Windows, Linux?) but that's not necessarily a bad thing. :-)