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Date:      Mon, 17 Apr 2000 22:50:20 -0400
From:      "Crist J. Clark" <cjc@cc942873-a.ewndsr1.nj.home.com>
To:        miy <miyako@sakr.net>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: network replies causing system messages flooding
Message-ID:  <20000417225020.A52719@cc942873-a.ewndsr1.nj.home.com>
In-Reply-To: <Pine.BSF.4.10.10004171838230.4331-100000@sakr.net>; from miyako@sakr.net on Mon, Apr 17, 2000 at 06:56:47PM -0400
References:  <20000416212801.C48499@cc942873-a.ewndsr1.nj.home.com> <Pine.BSF.4.10.10004171838230.4331-100000@sakr.net>

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On Mon, Apr 17, 2000 at 06:56:47PM -0400, miy wrote:
> On Sun, 16 Apr 2000, Crist J. Clark wrote:
> > On Sun, Apr 16, 2000 at 01:22:06AM -0400, miy wrote:
> > > 
> > > I originally had a windows box [10.0.0.2] connected to my cable connection
> > > through a FreeBSD gateway running natd. I recently added a second windows
> > > box to the network, and I it connects properly to the gateway, but I am 
> > > getting flooded by the following system message:
> > > 
> > > arp: 10.0.0.4 is on ed1 but got reply from 00:80:c8:e8:ea:d7 on rl0
> > > arp: 10.0.0.4 is on ed1 but got reply from 00:80:c8:e8:ea:d7 on rl0
> > > arp: 10.0.0.4 is on ed1 but got reply from 00:80:c8:e8:ea:d7 on rl0
> > > arp: 10.0.0.4 is on ed1 but got reply from 00:80:c8:e8:ea:d7 on rl0 
> > > 
> > > My natd configuration is as follows:
> > > /sbin/natd -s -n rl0 -redirect_port tcp 10.0.0.2:2121 2121
> > > /sbin/ipfw add 1000 divert 6668 ip from any to any via rl0
> > > /sbin/ipfw add 1002 divert 6668 ip from 10.0.0.2/24 to any via rl0
> > > 
> > > 
> > > #10.0.0.4 is the most recent windows box that was added to the network.
> > 
> > Well, if it weren't for the fact that you say that the 10.0.0.4 host
> > is on your net behind the NAT gateway, I would think that you
> > connected the 10.0.0.4 machine on the rl0 interface. Just to be safe,
> > how do you have the network physically configured? You don't have both
> > NICs on the gateway plugged into one hub or something like that,
> > right?
> > 
> > It could be that someone else on your cable LAN is leaking RFC 1918
> > addresses, and they make it over the modem to your machine. The modems
> > should not do that, but the idea of a poorly configured ISP, even a
> > coax cable one, never shocks me.
> 
> 
> My network is configured with the cable modem connected to my FreeBSD
> gateway machine (into rl0). The FreeBSD machine's second card (ed1) is 
> connected to my hub's uplink. The two windows boxes (10.0.0.2 & 10.0.0.4)
> are connected directly to the hub. 

Just a tiny point, if all of the devices connected to this hub are
NICs, you should not need to use an "uplink" port.

> I don't completely understand what leaking RFC 1918 addresses are. 
> Are these essentially leaked packets from my ISP's local subnet (other
> machines in my district) that are being collected by my gateway from the
> cable modem? Are these causing the problem or is it an issue of my
> physical configuration?

That packets from other machines could be reaching your NAT gateway
from the external net is a _possibility._ However, it is very
suspicious that the address happens to be one you are trying to use.

> My system message buffer now has 10 pages or so worth of:
> arp: 10.0.0.4 is on ed1 but got reply from 00:80:c8:e8:ea:d7 on rl0

Have you identified the piece of hardware associated with
00:80:c8:e8:ea:d7? Use this command,

  % arp -a

FYI, it's a piece of D-Link hardware.

Also, what is the configuration of each interface (output of 'ifconfig
interface' for both)?
-- 
Crist J. Clark                           cjclark@home.com


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