IPv6 temporary addresses

[Taylor R Campbell <campbell+netbsd%mumble.net@localhost>]

(I am not subscribed to this list, so please cc me in replies.)

If I set net.inet6.ip6.use_tempaddr to 1, NetBSD will randomly
generate IPv6 temporary addresses, but it will still by default choose
source addresses based on each interface's MAC address.

A cursory examination of the relevant parts of netinet6 reveals some
`#ifdef notyet' sections of the code handling another sysctl knob,
prefer_tempaddr, which would change the default choice of source
address.  It seems that these sections were intended to be included as
soon as some ndp-related support was committed later, but that whoever
intended to do that forgot about it.

FreeBSD has the prefer_tempaddr sysctl knob, and OpenBSD has some
per-interface ifconfig knobs based on RFC 4941, which is what the
internet-draft that FreeBSD's and NetBSD's temporary address support
was based on grew up into.

Can anyone familiar with the code comment on this?  I'd like to use
temporary addresses, and not broadcast my MAC address all over the
inter6tubes, but I'm hesitant to touch the code myself because it
looks pretty hairy.