ipv6 neighbor cache question

[神明達哉]

At Thu, 27 Mar 2014 17:23:55 +0100,
Mikal Sande <mikal at sande.im> wrote:

> Is the IPv6 neighbor cache supposed to not inlcude incomplete entries? When my freebsd box resolves a previously unknown ipv6 address with ndp it does not add anything to the neighbor cache before it gets a reachability confirmation. I have viewed the neighbor cache with ndp -a.
>
> The ipv6 addresses in question are local, so I am pretty sure that on-link determination is not interfering. The same thing happens with both link-local and global addresses.
>
> When I ping an unused ipv6 address I do not find any corresponding incomplete entry in the neighbor cache afterwards. But, if I ping an unused ipv4 address i do find an incomplete entry in the arp cache. I am curious as to why this behavior occurs. Is it intentional? Is it by design?
>
> The reason for my curiosity is that I have not observed this behavior in other OSes such as linux and openbsd.

I suspect that's something specific to recent versions of FreeBSD.
The very original kernel neighbor cache and ndp implementations of the
KAME project should have behaved as you expected above and actually
saw with OpenBSD.  I don't know if the change was intentional or a
kind of defect, though.  Hopefully someone more familiar with recent
updates in FreeBSD can clarify that.

--
JINMEI, Tatuya