rtadvd(8) and deprecated prefixes

[JINMEI Tatuya / 神明達哉]

>>>>> On Mon, 05 Feb 2007 16:56:49 -0800, 
>>>>> "Eugene M. Kim" <freebsd.org at ab.ote.we.lv> said:

> Note that the two automatically configured addresses on em0 are still
> preferred, while the prefix 2001:470:1f01:3222::/64 is deprecated on the
> router.

> I believe rtadvd(8) should advertise deprecated on-link prefixes with
> pltime of 0, but I still wanted to know what other people think about
> this before working on actual code.  So, here is the question: Is this
> really something to be fixed?

I'm pretty sure different people have different opinions on this
matter, but I personally think we should not try to "fix" it.

This feature originally intended to make rtadvd as much
configuration-free as possible in the most typical cases, that is, all
addresses on the router is configured by hand and the associated
prefixes are advertised with the default parameters defined in
RFC2461.  This is because why rtadvd does not allow the administrator
to specify just prefix lifetimes while letting the daemon get the
prefixes from the kernel.  So, treating a prefix lifetime of 0
separately is at least against the original design policy (believe me,
I'm confident because it's me who implemented this:-)

Also, once we open the Pandora's box, we'll encounter all other
non-default issues that beg customized behavior or require detailed
considerations on corner cases.  One example is to allow the user to
specify the lifetimes (without specifying prefixes).  We might also
want to have rtadvd follow decreasing lifetimes in real time.  Others
may want to restrict the advertised prefixes to some subset of ones
retrieved from the routing table, etc, etc.

So, (again) I'd personally keep the current feature and requires the
administrator to configure the router explicitly to handle any
non-default cases.  (If we agree on that) we may have to note in the
man page about the implementation policy, though.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					jinmei at isl.rdc.toshiba.co.jp