[NBLUG/talk] Strange ethernet issue

[Steve Johnson]

Yes, I physically checked the switch (Cisco switch.. not sure on
model).. Also just to be sure I ran mmap on the IP of one the boxes
when it was down and nothing came back.  I know pings are unreliable,
but nmap isn't supposed to use just IMCP, so it should have detected
something if someone got on my network.

I will try the arp queries after tonights reboot.. These machines are
production machines, so can't be down long in the middle of the day..
:)

-Steve


On Tue, Apr 10, 2012 at 9:54 AM, Kyle Rankin <kyle at nblug.org> wrote:
> 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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