Re: Enabling SLAAC for IPv6 by default

[Roy Marples <roy%marples.name@localhost>]

On 25/09/2018 16:40, Greg Troxel wrote:
> Roy Marples <roy%marples.name@localhost> writes:
>
> > He's specifically talking about temporary addresses.
> > dhcpcd enables stable private addresses by default instead.
>
> I am not quite following, and will assume I'm not the only one - so a
> few questions trying to be precise.
>
> I am unable to find any documentation of use_tempaddr and
> prefer_tempaddr under /usr/share/man.
>
> Is the "temp_addr" sysctl about "SLAAC privacy extensions", changing
> behavior of the in-kernel stateless autoconfiguration client, such that
> if not set, the MAC address is used to form the host part, and if set,
> forming the host part randomly?

No.
The MAC address forming the host part is still created.
A temporary address where the host part is random is *also* created.

> What is the lifetime of the addresses formed by the kernel when enabled?
> Are we following the recommendation of 1 day as preferred and 7 days as
> valid?

sysctls net.inet6.ip6.temppltime and net.inet6.ip6.tempvltime are used 
to calculate the lifetimes based on the lifetime of the actual address.

> Is there a mechanism to keep such addresses (marked deprecrated) until
> they are no longer in use (well, bound)?  I checked a few Mac machines,
> and they seem to keep "deprecated" addresses around for varying
> intervals.  Or simply the expiration at the end of the valid lifetime?

They will vanish when the lifetime expires.
This is my real issue, they are useless for persistent connections.

> I checked one each netbsd-7 and netbsd-8, configured for dhcpcd, and
> they have both link-local (fe80::) and global v6 addresses that do not
> appear to have been formed from the MAC address.

dhcpcd generates stable private addresses - not temporary addresses.
These are a different beast and a better solution than temporary addresses.
See RFC 7217.

> Do we know if there are mechanisms to keep temporary addresses in
> deprecated state while ?in use"?

Even if in use, they vanish when expired.
See my above issue.

Roy