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From: "Martin A. Brown" <mabrown-lartc@securepipe.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Snat Mac address changing
Date: Sat, 05 Apr 2003 18:36:19 +0000	[thread overview]
Message-ID: <marc-lartc-104956787617715@msgid-missing> (raw)
In-Reply-To: <marc-lartc-104956606216698@msgid-missing>

Chris,

  What does the physical interconnection of cables look like?
  Where is the arpwatch daemon?
  Do you have your public network and private network connected to
    the same hub/switch?

Could you give us a bit of ASCII art to show the configuration?

Judging from the symptoms, the only logical explanation I can imagine is
as follows.  You have your public and private networks connected to the
same medium (hub/switch).  Now, when a host on this network makes an ARP
request for 198.31.174.56, it might get two answers.

From any other box on the network try the following command:

# arping -I eth0 -c 3 198.31.174.56

See here for an explanation of ARP flux, if this is your problem:

  http://linux-ip.net/html/ether-arp.html#ether-arp-flux

Good luck,

-Martin

 : ok i have a program called arpwatch on the network, monitors arp/ipmatching,
 : it sees that the public side of  the Snat box has its mac address switch
 : between the public and private interface.
 : here i tried to provide most the information that i can think of.
 :
 : iptables v1.2.7a:
 : ____________________
 : Linux ns.highlandshighspeed.net 2.4.19-gentoo-r10 #5 Sun Mar 9 16:53:57 PST
 : 2003
 :  i686 Intel(R) Pentium(R) 4 CPU 1.60GHz GenuineIntel GNU/Linux
 : _____________________________
 : /bin/echo 1 > /proc/sys/net/ipv4/ip_forward
 : iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to-source 198.31.174.56
 : __________________________
 : Chain PREROUTING (policy ACCEPT)
 : target     prot opt source               destination
 :
 : Chain POSTROUTING (policy ACCEPT)
 : target     prot opt source               destination
 : SNAT       all  --  anywhere             anywhere           to:198.31.174.56
 :
 : Chain OUTPUT (policy ACCEPT)
 : target     prot opt source               destination
 : __________________________
 : eth0      Link encap:Ethernet  HWaddr 00:04:75:A0:DE:59
 :           inet addr:a.b.c.d  Bcast:198.31.174.255  Mask:255.255.255.0
 :           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
 :           RX packets:18320637 errors:0 dropped:0 overruns:1 frame:0
 :           TX packets:18395481 errors:0 dropped:0 overruns:0 carrier:0
 :           collisions:0 txqueuelen:100
 :           RX bytes:3151929956 (3005.9 Mb)  TX bytes:4285940372 (4087.3 Mb)
 :           Interrupt:11 Base address:0xe400
 :
 : eth1      Link encap:Ethernet  HWaddr 00:04:75:A0:DD:F9
 :           inet addr:A.B.C.D  Bcast:192.168.33.255  Mask:255.255.255.0
 :           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
 :           RX packets:20321245 errors:0 dropped:0 overruns:5 frame:0
 :           TX packets:18611116 errors:0 dropped:0 overruns:0 carrier:0
 :           collisions:0 txqueuelen:100
 :           RX bytes:768762048 (733.1 Mb)  TX bytes:3808977459 (3632.5 Mb)
 :           Interrupt:10 Base address:0xe800

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

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  reply	other threads:[~2003-04-05 18:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-04-05 18:06 [LARTC] Snat Mac address changing Chris K Ellsworth
2003-04-05 18:36 ` Martin A. Brown [this message]
2003-04-05 21:39 ` Chris K Ellsworth

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