"Jose M. Alcaide" wrote:
> I found something interesting: these messages are caused by ARP requests
> carrying as the sender IP address. All of them come from Apple
> Macintosh (over 40 different machines). I am not sure whether is a
> legal sender IP address in an ARP request; means "this" host, so
> that I think that it is a valid address when the machine doing the ARP
> request does not know its IP address yet (though this sounds stupid).

Most likely, these are ARPs for multicast for SLPv2 location
of network resources, such as default gateway, etc., prior to
stateless autoconfiguration.

We discussed doing this on one of the IETF lists, as a side issue
to IPv6 stateless autoconfiguration, which ends up giving you a
routable address, in the context of permitting the reverse
address to be set to a machine name outside your domain for a
machine who got a routable stateless address from your domain.

You may also want to look at the ZEROCONF working group list

> Anyway, the fact is that -CURRENT can flood the console and
> /var/log/messages if there are many Macintosh sending these ARP requests
> in a LAN (as it is our case). I think that there is no reason to printf
> these messages, since is a valid IP address meaning "this" host.

Yes.  This is basically a required use for a "whohas" for doing
stateless autoconfiguration, both in IPv6 (routable) and IPv4
(in the presence of a NAT).

The most recent DHCP and autoconfiguration RFC lets you ignore
DHCP entirely, and it lets you have a DHCP server refuse an
address to the host, with no recourse for the host to do the
autoconfiguration (e.g. a properly configured DHCP server can
make a conforming client not get an address at all).  I don't
think that, in that case, leaving the machine at is a
valid thing to do: the interface should probably be forced down

That said, it's probably a good idea to never ARP for,
since a "who has" in that case is a really dumb idea, since,
as weas pointed out, it's intended to mean "this host", in the
absence of an IP address (i.e. is not an IP address,
it's a special value meaning "not an IP address").

-- Terry

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