Date: Fri, 19 Oct 2001 11:12:48 +0200 (CEST) From: Harti Brandt <brandt@fokus.gmd.de> To: Terry Lambert <tlambert2@mindspring.com> Cc: "Jose M. Alcaide" <jose@we.lc.ehu.es>, Beech Rintoul <akbeech@anchoragerescue.org>, <current@FreeBSD.ORG>, <net@FreeBSD.ORG> Subject: Re: arp: <some ether addr> is using my IP address 0.0.0.0! ??!?!? Message-ID: <20011019110116.Y1072-100000@beagle.fokus.gmd.de> In-Reply-To: <3BCEEBDD.46121235@mindspring.com>
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On Thu, 18 Oct 2001, Terry Lambert wrote:
TL>To expand a little...
TL>
TL>> That said, it's probably a good idea to never ARP for 0.0.0.0,
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. 0.0.0.0 is not an IP address,
TL>> it's a special value meaning "not an IP address").
TL>
TL>It's probably also a good idea to make interfaces who have an
TL>IP of 0.0.0.0 _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 0.0.0.0:
18:33:51.222688 arp who-has hydra tell 0.0.0.0
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 0.0.0.0 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 address 0.0.0.0!
I think this is because I have an interface that is up and has NO IP
address:
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet 127.0.0.1 netmask 0xff000000
xl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet 193.175.135.70 netmask 0xffffff00 broadcast 193.175.135.255
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 0.0.0.0
harti
TL>Ghah. I hate special cases...
everything is a special case...
harti
TL>
TL>-- Terry
TL>
TL>To Unsubscribe: send mail to majordomo@FreeBSD.org
TL>with "unsubscribe freebsd-net" in the body of the message
TL>
--
harti brandt, http://www.fokus.gmd.de/research/cc/cats/employees/hartmut.brandt/private
brandt@fokus.fhg.de
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