[NBLUG/talk] Strange ethernet issue

Kyle Rankin kyle at nblug.org
Tue Apr 10 09:54:35 PDT 2012


On Tue, Apr 10, 2012 at 09:40:31AM -0700, Steve Johnson wrote:
> Hi Guys,
> 
> I am running 3 linux boxes all on the same network, running static 10
> net addresses, each on their own IP address..  A strange thing has
> started happening about a month ago, if I reboot the box when the
> system comes up at the point when it tries to bring up the eth0
> interface I get an error "IP Address in use by another host" and then
> the interface does not come up.  Loggin in from the console as root
> and running ifup eth0 gives me the same error.  The only way I can get
> the interface to come up is to physically unplug the ethernet, then
> run ifup eth0, that brings up the eth0 correctly, and then plug the
> ethernet cable back in.. Then it runs fine until another reboot (Or if
> I ifdown eth0 I will have the same problem)..
> 
<snip>
> 
> Ay ideas, or clues would be greatly appreciated.. I've been trying to
> trouble shoot this for over a month now with now luck.
> 
> -Steve
> 

Are you absolutely sure that only one host truly has those IP addresses on
that subnet? When the host comes up and tries to assign the IP addresses to
itself, it will first perform an ARP and see if another MAC address on the
network claims to have that IP. What I would do is take down one of the
hosts, then from a different machine run ARP queries for those 10 IPs
belonging to the first host and see if the MAC address you get back is the
correct one. If your networking guys are trying to do anything fancy with
NAT and misconfigured something, it could be that your switch is claiming
to have those IPs (it's easy to check, an arp query against one of the IPs
will return back a MAC belonging to a Cisco, HP, or whatever switch you
have).

-- 
Kyle Rankin
NBLUG President
The North Bay Linux Users' Group
http://nblug.org
IRC: greenfly at irc.freenode.net #nblug 
kyle at nblug.org



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