On Thu, 18 Oct 2001, Terry Lambert wrote:

TL>To expand a little...
TL>> That said, it's probably a good idea to never ARP for,
TL>> since a "who has" in that case is a really dumb idea, since,
TL>> as weas pointed out, it's intended to mean "this host", in the
TL>> absence of an IP address (i.e. is not an IP address,
TL>> it's a special value meaning "not an IP address").
TL>It's probably also a good idea to make interfaces who have an
TL>IP of _not_ respond to ARP requests for that address,
TL>and, just in case there are other idiots, we should also not
TL>give proxy ARP responses for that address, etiher.

I have run tcpdump all night to find out what happens. The host receives
an ARP request with a source address of

18:33:51.222688 arp who-has hydra tell
                         0001 0800 0604 0001 0030 65c6 a174 0000
                         0000 0000 0000 0000 c1af 8755 5555 5555
                         5555 5555 5555 5555 5555 5555 5555

I think, this may happen if the host does not yet know it's IP address
(DHCP maybe?).

But FreeBSD-current for some unknown reason answers to this request:

18:33:51.222835 arp reply is-at 0:60:97:a:99:f
                         0001 0800 0604 0002 0060 970a 990f 0000
                         0000 0030 65c6 a174 0000 0000 5555 5555
                         5555 5555 5555 5555 5555 5555 5555

and then prints:

Oct 18 18:33:51 scotty /boot/kernel/kernel: arp: 00:30:65:c6:a1:74 is using my IP 

I think this is because I have an interface that is up and has NO IP

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet netmask 0xff000000
        inet netmask 0xffffff00 broadcast
        ether 00:60:97:0a:99:0f
        media: Ethernet 10baseT/UTP (10baseT/UTP <half-duplex>)

hatm0: flags=841<UP,RUNNING,SIMPLEX> mtu 9180
        media: ATM UTP/155MBit
        status: active
lane0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1516
        ether 00:00:00:00:00:00

I think it is definitly wrong to assume that an interface with no IP
address has IP address


TL>Ghah.  I hate special cases...

everything is a special case...


TL>-- Terry
TL>To Unsubscribe: send mail to [EMAIL PROTECTED]
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harti brandt, http://www.fokus.gmd.de/research/cc/cats/employees/hartmut.brandt/private
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